NHS Choices

Can a yoghurt a day reduce diabetes risk?

NHS Choices - Behind the Headlines - Tue, 25/11/2014 - 11:20

"Eating a small portion of yoghurt every day may reduce diabetes risk," The Independent reports.

This news comes from a US study that assessed the eating habits of more than 100,000 people and then followed them up every four years, looking for new diagnoses of type 2 diabetes.

Pooling the results of this study with 14 other studies, the researchers estimated each serving of yoghurt – 244 grams (g) – a day decreased the risk of developing type 2 diabetes by around 18%.

There was no significant link between total dairy intake or intake of other specific dairy products and type 2 diabetes.

A challenge facing this and similar studies is making sure all relevant outside influencing factors (confounders) have been accounted for, which is very tricky to do in practise.

If this has not been done conclusively, yoghurt consumption may be acting as a marker of a healthier lifestyle in general and has no direct influence on diabetes risk, which may be the case here.

We also don't know what sort of yoghurt the participants consumed. For example, many low-fat yoghurts are very high in sugar, which could contribute to weight gain.

It is therefore possible yoghurt may reduce the risk of developing diabetes, but may increase the risk of other diseases.

Current advice to reduce the risk of type 2 diabetes remains the same: eat a healthy diet, maintain a healthy weight, avoid smoking, moderate alcohol consumption, and take regular exercise.

 

Where did the story come from?

The study was carried out by researchers from Harvard School of Public Health and was funded by the US National Institutes of Health.

One of the study's authors declared a competing interest as he "holds membership of Unilever North America Scientific Advisory Board".

Unilever produces a huge number of commonly eaten yoghurts. It is not clear to what extent this conflict of interest may have influenced the study design, methodology or interpretation.

The study was published in the peer-reviewed medical journal BioMed Central (BMC) Medicine. It is an open access journal, meaning that anyone can read the full research publication for free.

Generally, the media reported the study accurately. But many sources chose to suggest that, "it might be a good idea to eat yoghurt regularly" without due consideration for the potential downsides of this advice.

For example, eating low-fat, high-sugar yoghurt may contribute to weight gain and weight-related diseases other than type 2 diabetes. It could also potentially increase the risk of tooth decay, particularly in children.

It also wasn't made clear what type of yoghurt was consumed, or that the association between yoghurt and diabetes may still be influenced by other factors.

 

What kind of research was this?

This was a meta-analysis combining the results of three large prospective cohort studies.

The researchers attest that the relation between the consumption of different types of dairy and the risk of type 2 diabetes remains uncertain.

They therefore aimed to evaluate the association between total dairy and individual types of dairy consumption and incident type 2 diabetes in US adults.

Type 2 diabetes is a condition where the person can't control their blood glucose, either because the body doesn't produce enough insulin or the body's cells don't react to insulin.

The rapid rise in the number of adults in Westernised nations such as the UK developing type 2 diabetes is caused by:

  • increasing obesity levels
  • a lack of exercise
  • an increase in unhealthy diets
  • an ageing population

Read more about risk factors for type 2 diabetes.

 

What did the research involve?

The research team used existing data on 41,436 men in the Health Professionals Follow-Up Study (1986-2010), 67,138 women in the Nurses' Health Study (1980-2010), and 85,884 women in the Nurses' Health Study II (1991-2009) to look at the links between diet and type 2 diabetes.

Diet was assessed by validated food frequency questionnaires and data was updated every four years. Incident type 2 diabetes was confirmed by a validated supplementary questionnaire.

Every two years, data was gathered and updated on risk factors for chronic diseases, such as body weight, cigarette smoking, physical activity, medication use and family history of diabetes, as well as history of chronic diseases such as high blood pressure and high cholesterol.

Among participants in the two nurse studies, information on menopausal status, post-menopausal hormone use and oral contraceptive use was also gathered.

The researchers analysed their results in three phases, with each phase adjusting for more and more potentially confounding factors.

The fully adjusted analysis took account of the following potential confounders:

  • age
  • calendar time with updated information at each two-year questionnaire cycle
  • body mass index (BMI)
  • total energy intake
  • race
  • smoking
  • physical activity
  • alcohol consumption
  • menopausal status
  • menopausal hormone use (Nurses' Health Study II participants only)
  • oral contraceptive use (Nurses' Health Study II participants only)
  • family history of diabetes
  • diagnosed with high blood pressure or high cholesterol at baseline
  • trans-fat intake (a type of unsaturated fat often found in processed foods)
  • glycaemic load (eating foods known to raise blood glucose levels)

As well as intakes of:

  • red and processed meat
  • nuts
  • sugar-sweetened beverages
  • coffee
  • other types of dairy foods

The team extended their work by conducting an updated meta-analysis that combined the new results from the three large cohort studies described above with findings from previous studies.

This previous research included prospective studies with cohort, case cohort or nested case-control design investigating the association between the intake of dairy products and the risk of type 2 diabetes. Literature was searched for up until October 2013.

In studies that reported the intakes by grams (g), they used 177g as a serving size for total dairy products, and 244g as a serving size for milk and yoghurt intake to recalculate the intakes to a common scale (servings per day).

 

What were the basic results?

During 3,984,203 person years of follow-up, they documented 15,156 cases of incident type 2 diabetes.

After adjustment for age, BMI and other lifestyle and dietary risk factors, total dairy consumption was not associated with type 2 diabetes risk.

The pooled hazard ratio (HR) (95% confidence interval [CI] of type 2 diabetes for one serving per day increase in total dairy was 0.99, 95% CI 0.98 to 1.01), so the this result was not statistically significant.

Among different types of dairy products, neither low-fat nor high-fat dairy intake was appreciably associated with risk of type 2 diabetes.

However, yoghurt intake was consistently and inversely associated with type 2 diabetes risk across the three cohorts with a pooled HR of 0.83 (95% CI 0.75 to 0.92) for one serving per day increment (trend analysis).

For added validity, they conducted a meta-analysis of 14 additional prospective cohorts with 459,790 participants and 35,863 incident type 2 diabetes cases.

The pooled relative risks (RRs) (95% CIs) were 0.98 (0.96, 1.01) and 0.82 (0.70, 0.96) for one serving of total dairy per day and one serving of yoghurt per day, respectively.

 

How did the researchers interpret the results?

The researchers' main conclusion was that, "Higher intake of yoghurt is associated with a reduced risk of T2D [type 2 diabetes], whereas other dairy foods and consumption of total dairy are not appreciably associated with incidence of T2D."

They added that, "The consistent findings for yoghurt suggest that it can be incorporated into a healthy dietary pattern. However, randomised clinical trials are warranted to further examine the causal effects of yoghurt consumption, as well as probiotics on body weight and insulin resistance."

 

Conclusion

This analysis of three large cohort studies, and a meta-analysis of 14 more, came up with estimates that each serving per day of yoghurt (244g) decreases the relative risk of developing type 2 diabetes by 18%.

It suggests other dairy foods and consumption of total dairy are not associated with type 2 diabetes. It was not clear over what time period this risk reduction was achieved, as follow-up times varied, but the maximum was 30 years.

The research team pointed out that their findings on total dairy intake were consistent with some, but not all, previous studies. Differences between this and previous studies may be because the current study used longer-term follow-up (more than 10 years).

The study had a number of strengths, including its large sample size, use of prospective data and ability to take account of a large number of confounding factors. 

But, as with all studies, there are also limitations to consider.

What sort of yoghurt was consumed?

Firstly, what sort of yoghurt we are talking about here? Greek, natural or added sugar, low-fat or full-fat?

From the study data presented, there are few distinctions made and all types of yoghurt are lumped together in the analysis.

This means it is not possible to know which types of yoghurt are potentially beneficial. This may depend on the levels of sugar, fat and probiotic bacteria, or other constituents.

For example, many low-fat yoghurts are very high in sugar, which could contribute to weight gain and increase the risk of harms from other weight-related diseases.

Other health outcomes not considered

This study focused exclusively on the risk of developing type 2 diabetes. The effect of diet on other diseases was not studied, so any compensating effects would go unnoticed.

For example, those eating yoghurt may be at a reduced risk of developing type 2 diabetes, but at an increased risk of developing another disease.

Were all the confounders accounted for?

Also, despite adjusting for a number of potential confounding factors, it's difficult to know whether all relevant factors have been fully accounted for.

Yoghurt consumption may be a marker of a healthy lifestyle in general, which could be associated with reduced risk of this chronic disease.

This result seems to be consistently found across the three large cohort studies and 14 other studies, which gives it some credibility.

But a systematic review and meta-analysis would be the best way to assess the link. This would ensure that all relevant material is considered. There is no guarantee that important studies were excluded from the meta-analysis of the current study, which could influence its findings.

This type of study typically feeds into the development or updating of national guidelines, which consider all the available evidence before deciding on what dietary advice to give the public. 

For now, current lifestyle advice to reduce the risk of type 2 diabetes remains the same: aim for a balanced diet high in fruit and vegetables and low in sugar, salt and saturated fats, take regular exercise in line with recommendations, avoid smoking, and moderate your alcohol consumption.

Read more about what eating a healthy, balanced diet entails. 

Analysis by Bazian. Edited by NHS ChoicesFollow Behind the Headlines on TwitterJoin the Healthy Evidence forum.

Links To The Headlines

A yoghurt a day could reduce your risk of diabetes, scientists find. The Independent, November 24 2014

How yoghurt could stave off diabetes: Just two spoonfuls a day cut odds of developing the disease by a fifth. Daily Mail, November 25 2014

A yoghurt a day may cut diabetes risk. The Times, November 25 2014

A yoghurt a day keeps diabetes away, say scientists. Daily Mirror, November 25 2014

A tablespoon of yoghurt could be key to beating diabetes, reveals new study. Daily Express, November 25 2014

Links To Science

Chen M, Sun Q, Giovannucci E, et al. Dairy consumption and risk of type 2 diabetes: 3 cohorts of US adults and an updated meta-analysis. BMC Medicine. Published online November 25 2014

Categories: NHS Choices

Therapy reduces risk of suicide or self-harm

NHS Choices - Behind the Headlines - Mon, 24/11/2014 - 11:30

“Talk therapy sessions can help reduce the risk of suicide among high-risk groups,” BBC News reports.

The headline is prompted by a large Danish study that took place over a 20-year period.

Researchers matched those who had received different psychosocial (“talking therapy”) interventions after a self-harm attempt with those who had not received a psychosocial intervention, and then compared relevant outcomes.

People who received psychological interventions had reduced risk of further self-harm, but not suicide, within the first year. Looking at longer-term follow-up, psychological interventions were associated with reduced risk of both self-harm and suicide.

However, it may be difficult to isolate the direct effect of the psychological intervention. People who had received psychological interventions were recruited from treatment clinics that required them not to be in need of psychiatric admission.

Meanwhile, those who did not receive psychological treatment were reported to include people who needed psychiatric admission, or chose not to receive suicide prevention treatment. These factors could mean that this comparison group were at increased risk of subsequent harm and death to begin with.

Also, the situation in the UK might be slightly different to Denmark. Despite this, any research that could help prevent suicides is always valuable.

 

Where did the story come from?

The study was carried out by researchers from the University of Copenhagen in Denmark and the Johns Hopkins Bloomberg School of Public Health in the US, in addition to other research institutions in Denmark and Norway. Funding was provided by the Danish Health Insurance Foundation; the Research Council of Psychiatry, Region of Southern Denmark; the Research Council of Psychiatry, Capital Region of Denmark; and the Strategic Research Grant from Health Sciences, Capital Region of Denmark.

The study was published in the peer-reviewed medical journal The Lancet Psychiatry.

BBC News was generally representative of the research’s findings, but inaccurately described participants as having “attempted suicide”. The research included participants who had self-harmed. Not all instances of self-harm are suicide attempts, so it is a mistake to conflate the two terms. For some people, certain types of self-harming, such as cutting, are a way of coping with overwhelming emotional distress, rather than an attempt to end their life.

It was not clear from the study what proportion of the self-harming events were attempted suicide.

 

What kind of research was this?

This was a cohort study comparing people who did and did not receive a psychosocial (talking) therapy after deliberate self-harm, and examined the outcomes of further self-harm, suicide or death from other causes. 

The researchers say that self-harm is a strong predictor of suicide. Research indicates that within the first year after self-harming, about 16% of people self-harm again; 0.5 to 1.8% die by suicide; and 2.3% die from another cause. However, evidence for the effectiveness of psychological interventions following self-harm is said to be missing, and this study aimed to investigate this.

 

What did the research involve?

This study compared people in Denmark who received a psychological intervention following a first episode of self-harm with those who received standard care, over the 18-year period between January 1992 and December 2010. They calculated the risk of repeated self-harm, suicide and dying of any cause after the first instance of self-harm, and compared the risks between the two groups for differences that might be due to the psychological intervention. 

The people who received psychological interventions were identified from one of seven suicide prevention clinics in Denmark. These clinics are said to receive people who are thought to be at risk of suicide, but not in need of psychiatric admission or other outpatient programmes. For the purposes of this study, participation was considered to be attendance for at least one psychological treatment session that was focused on suicide prevention. The seven different clinics used various types of therapy, including cognitive, problem-solving, crisis, dialectical behaviour, integrated care, psychodynamic, systemic, psychoanalytic approaches and support from social workers.

The controls who did not receive a psychological intervention were people who had presented to hospital with an episode of self-harm during the study period, but who did not receive any psychological intervention. They could receive any form of standard care, including admission to a psychiatric hospital, referral to outpatient treatment or a general practitioner, or discharge without referral.

The reasons why these people did not receive a psychological intervention were variable, including:

  • living in an area remote from services
  • being referred for other treatment (including hospital admission)
  • not wanting to be referred for suicide prevention treatment

All people were linked via their Danish ID numbers to the Danish Civil Register, National Registry of Patients, Psychiatric Central Registry and Registry of Causes of Death. Follow-up was to the end of 2011, giving a follow-up period for the people in the study of 1 to 20 years.

The main outcomes examined were self-harm, death by suicide, and death by any cause. People who did and did not receive psychological interventions were matched for various potentially confounding factors, including:

  • study period (1992 to 2000 or 2001 to 2011)
  • age
  • gender
  • educational level
  • socioeconomic status
  • previous episodes of self-harm
  • specific psychiatric diagnoses

 

What were the basic results?

The study included a total of 5,678 people in the psychological intervention group and 17,034 matched people who had not received a psychological intervention after self-harm. Around two-thirds were women and most were in the 15 to 49 age bracket. Around 10% had a previous episode of self-harm.

During the first year of follow-up, 6.7% of people receiving a psychological intervention had a repeated self-harm attempt, compared with 9.0% of the no psychological intervention group. Psychosocial therapy was associated with a 27% reduced risk of self-harm within one year (odds ratio (OR) 0.73, 95% confidence interval (CI) 0.65 to 0.82). The absolute risk reduction (ARR), measuring how much the risk of self-harm is reduced in those who received the psychosocial therapy, was 2.3% (95% CI 1.5 to 3.1%). The number needed to treat (NNT) was 44 (95% CI 33 to 67), indicating that 44 people would need to receive psychosocial therapy after a self-harm attempt to prevent one person self-harming within one year.

There was no significant difference between groups in rates of suicide within one year, but overall mortality rates within one year were slightly lower in the psychological intervention group (1,122 compared with 1,824 per 10,000), which also meant a significant reduction in overall mortality rate (OR 0.62, 95% CI 0.47 to 0.82). When considering the longer term effects over the full 20 years of follow-up, psychological intervention was associated with a 16% decreased risk of repeated self-harm (OR 0.84, 95% CI 0.77 to 0.91), with an ARR of 2.6% (95% CI 1.5to 3.7) and NNT of 39 people (95% CI 27 to 69).

When looking at overall follow-up, psychological therapy was also associated with a 25% reduced risk of death from suicide (OR 0.75, 0.60 to 0.94), with an ARR of 0.5% (95% CI 0.1 to 0.9) and a NNT of 188 people to prevent one suicide (95% CI 108 to 725). It was also associated with significant reduction of death from any cause (OR 0.69, ARR 2.7%, NNT 37).

The results altogether suggested that during the 20 years of follow-up, 145 self-harm episodes and 153 deaths were prevented by psychological interventions, with 30 of these deaths from suicide.

 

How did the researchers interpret the results?

The researchers conclude that their findings, “show a lower risk of repeated deliberate self-harm and general mortality in recipients of psychosocial therapy after short-term and long-term follow-up, and a protective effect for suicide after long-term follow-up, which favour the use of psychosocial therapy interventions after deliberate self-harm”.

 

Conclusion

The researchers report that this is the largest follow-up study of psychosocial interventions offered after deliberate self-harm attempts. Compared to standard care, it found that psychosocial interventions were associated with a reduced risk of repeated self-harm and death from any cause within the first year of follow-up. In the longer term, psychosocial interventions were associated with reduced risks of self-harm, death from any cause and suicide, specifically.

The study benefits from its large sample size, long duration of follow-up and reliable methods of identifying participants and their outcomes. There are, however, some points to be considered when interpreting the findings.

Possible selection bias

The reasons that people did not receive a psychological treatment could have put them at higher risk of subsequent harm to start with, potentially explaining all or some of the risk difference between the two groups. Though the people who did and did not receive psychological treatments were matched for various factors, this may not have been comprehensive, and some selection bias may still be present. For example, all the people who were receiving psychological treatments had been referred to suicide prevention clinics because they were not considered to be in need of psychiatric admission or other outpatient treatment following their self-harm attempt. Meanwhile, those who did not receive psychological treatment were reported to include people who needed psychiatric admission, or chose not to receive suicide prevention treatment after their self-harm attempt.

This makes it difficult to isolate the effect of the psychological intervention compared with selection biases and other confounding factors. It could be that the reduced risk seen in the psychological intervention group is not solely a result of the intervention, but that there were other risk factors among the non-treated group that were increasing their risk of further self-harm/suicide attempts and so confounding the association.

However, some degree of selection bias is inevitable in this type of study. The only way to remove it completely would be to randomise people to treatment or no treatment, which could never be done for ethical reasons.

Uncertainty about most effective intervention

It is also difficult to conclude many treatment implications from this study in terms of what would be the best type of psychological intervention to use after a self-harm attempt (a wide variety of interventions were used in this study), whether the optimal type differs according to the individual (e.g. according to mental health diagnosis[es]), and what would be the optimal treatment duration.

Results may not be applicable to the UK

The results also apply to Denmark, which may differ from other countries – for example, in terms of healthcare and mental health services, and population health, psychosocial and environmental influences. This may mean that the results are less applicable to this country.

People in the UK who present to health services following self-harm or a suicide attempt receive assessment by specialist mental health professionals, followed by referral, hospital admission or discharge, and follow-up care and treatment as appropriate to their individual situation.

Getting help

If you are reading this because you are having suicidal thoughts, try to ask someone for help. It may be difficult at this time, but it's important to know you are not beyond help and you are not alone.

Speak to a person you trust (such as a friend or family member), make an urgent appointment with your GP or contact your local A&E department. The Samaritans (08457 90 90 90) also operates a 24-hour service available every day of the year.

Read more about getting help for suicidal or self-harming thoughts, as well as spotting possible warning signs in family members and friends.

Analysis by Bazian. Edited by NHS ChoicesFollow Behind the Headlines on TwitterJoin the Healthy Evidence forum.

Links To The Headlines

Suicide risk reduced after talk therapy, study suggests. BBC News, November 24 2014

Talking therapy 'can stop suicide'. Mail Online, November 24 2014

Links To Science

Erlangsen A, Lind BD, Stuart EA, et al. Short-term and long-term effects of psychosocial therapy for people after deliberate self-harm: a register-based, nationwide multicentre study using propensity score matching. The Lancet Psychiatry. Published online November 24 2014

Categories: NHS Choices

Vegetarian diet 'could have slight benefits in diabetes'

NHS Choices - Behind the Headlines - Mon, 24/11/2014 - 11:30

"Vegetable diet will beat diabetes: Meat-free lifestyle cures killer disease," is the typically overblown headline in the Daily Express.

But researchers actually found a vegetarian diet led to a quite modest fall in only one measure of blood glucose called HbA1C, a measure of blood glucose control.

The paper reports on a systematic review which combined the results of six trials that involved 255 people with type 2 diabetes. They examined whether vegetarian or vegan diets improved blood glucose control compared with a control diet.

Overall, the pooled results of five of these trials found a vegetarian or vegan diet reduced HbA1c by 0.39%. There was no significant effect on fasting glucose levels, an assessment of how efficiently the body can process glucose in the short term.

This slight reduction in HbA1c is no cure. As the researchers themselves pointed out, the reduction is less than you would expect if a patient was being treated with the drug of choice for type 2 diabetes, metformin.

This review also has various important limitations, including the variable design and quality of the six trials included. So, it does not prove that a vegetarian or vegan diet is better for a person with type 2 diabetes, and any media claims of a "cure" for the condition are entirely baseless.

 

Where did the story come from?

The study was carried out by researchers from Keio University in Japan and The George Washington University School of Medicine in the US.

Funding was provided by the Japan Society for the Promotion of Science and the Nestlé Nutrition Council, Japan.

One of the co-authors declared a non-financial conflict of interest. This author serves as president of the Physicians Committee for Responsible Medicine, without financial compensation.

This organisation is described in the publication as one that, "promotes the use of low-fat, plant-based diets and discourages the use of animal-derived, fatty, and sugary foods". This represents a potential conflict of interest in the interpretation of the results.

The study was published in the peer-reviewed medical journal, Cardiovascular Diagnosis and Therapy and the study is open access, so it is free to read the study online.

The Daily Express' coverage of the study is accurate and contains some useful background information, so it is frustrating that its headline is totally misleading, especially as it was on the front page.

In fact, this review of studies found vegetarian or vegan diets caused a slight reduction in HbA1c compared with non-vegetarian diets. This is not a cure in any sense of the word.

The current thinking is that there is no such thing as a cure for type 2 diabetes. The condition can be successfully managed, but not cured.

The study is also only applicable to type 2 diabetes, so the headlines do not apply to type 1 diabetes.

 

What kind of research was this?

This was a systematic review and meta-analysis combining the results of controlled trials that examined the effects of vegetarian diets on blood sugar control in type 2 diabetes.

As the researchers say, previous research has suggested a link between a vegetarian diet and improved blood sugar control, but the relationship is not well established.

As an interesting aside, the researchers highlight how diabetes levels were found to be lower in Seventh-day Adventists, a Protestant Christian denomination whose followers are encouraged to adopt a vegetarian diet.

This review aimed to examine this grey area. A systematic review and meta-analysis of randomised controlled trials is the best way of examining the evidence to date that has assessed this question.

 

What did the research involve?

The researchers searched a number of literature databases (from their inception to 2013) to identify published clinical trials examining the effects of a vegetarian, vegan or omnivorous diet on blood sugar control in people with type 2 diabetes who were over the age of 20.

A vegetarian diet was defined as one excluding meat, poultry and fish, while a vegan diet excluded all animal products.

Eligible trials had an intervention duration of at least four weeks and examined the main outcome of changes in HbA1c.

This gives an indication of blood sugar control in the longer term, as it indicates the amount of sugar being carried by red blood cells, which have a lifespan of around three months. Change in fasting blood sugar measures was a secondary outcome.

In an added effort to find all relevant information for the review, the research team scoured the reference lists of all articles they found from the search of electronic databases, and also contacted research experts for additional material.

The researchers assessed the quality of the studies included, and pooled studies calculating the average difference in HbA1c and fasting blood sugar between vegetarian or vegan and comparison diets.

 

What were the basic results?

A total of six trials met the inclusion criteria, involving 255 people with type 2 diabetes with an average age of 52-and-a-half. The average trial duration was 23.7 weeks, or about six months.

Five of the studies examined vegan diets and one studied vegetarian diets. Four trials were conducted in the US, one in Brazil and one in the Czech Republic.

Of the six studies, three were randomised controlled trials, one was a cluster randomised controlled trial, and two were non-randomised controlled trials.   

In the pooled analysis of five trials, the vegetarian or vegan diet was associated with a significant reduction in HbA1c (-0.39%, 95% confidence interval [CI] -0.62 to -0.15) compared with omnivorous control diets.

But the pooled analysis of four trials did not find a statistically significant reduction in fasting blood sugar: the average difference with the vegetarian or vegan diet compared with control was -0.36 mmol/L, 95% CI -1.04 to 0.32.

Compared with control, the vegetarian or vegan diets were also associated with significant reductions in the amount of total energy the diet provided, either through carbohydrate, protein, total fat, cholesterol and fibre.

 

How did the researchers interpret the results?

The researchers concluded that, "Consumption of vegetarian diets is associated with improved [blood glucose] control in type 2 diabetes."

 

Conclusion

This systematic review has identified six trials assessing whether vegetarian or vegan diets improve blood sugar control in type 2 diabetes compared with control.

It found the vegetarian or vegan diet gave significant improvement in one measure of blood sugar control (HbA1c), but not in another (fasting blood glucose).

However, there are some important limitations to consider before we can categorically conclude that people with type 2 diabetes should switch to a meat and fish-free diet:

The improvement in blood sugar control was quite small

The pooled results of five trials found a vegetarian or vegan diet was associated with a 0.39% reduction in HbA1c, but we don't know that this would have made any meaningful clinical difference in diabetes control for the individual.

Overall, although any reduction is likely to be a good thing, the precise benefit would depend on what a person's HbA1c level was to start with.

The target HbA1c is usually set at a level below around 7%, so it may be more useful knowing whether a vegetarian or vegan diet improved the proportion of people achieving their target HbA1c level. The review also found no improvement in fasting blood glucose control.

The intervention diets were varied

Despite the publication tending to refer to the intervention diets as vegetarian, they were actually quite varied across the trials.

Four of the trials were described as low-fat vegan, one as lacto-vegetarian (a diet that includes dairy products but not eggs), and one lacto-ovo low-protein (similar to a lacto-vegetarian diet but, as the name suggests, with a focus on low-protein foods).

The control diets were also quite varied across the trials

The researchers included diets described as omnivorous, low fat, "diabetic diet" and those that followed American Diabetic Association guidance.

Overall, this doesn't give a very clear picture of what diets were being compared, which makes it hard to conclude that a particular diet is associated with an improvement in blood sugar control compared with a particular control.

The trials had variable quality evidence

Only three of the six trials studied were true randomised controlled trials. They varied in the duration of the dietary intervention between four and 74 weeks.

Also, only one of the six trials (a controlled trial) is reported to have made any adjustment for potential confounders (sex, baseline HbA1c level and medication). The others report no adjustment.

We also don't know how the trials checked that the diets were being followed as assigned, or of any other intervention or advice that may have been given to the participants alongside the dietary intervention (such as advice about physical activity).

The review only included published trials

In their assessment of possible publication bias, the researchers observed that smaller trials that found reductions in HbA1c level were perhaps more likely to have been published and therefore included in this review.

The small number of participants

Despite this being a systematic review of trials, the total number of participants was still quite small, at only 255. This is a very small number of patients, and it might be unwise to base any firm or generalisable conclusions on such small numbers.

A vegetarian or vegan diet can be a healthy lifestyle choice for a person with type 2 diabetes if it provides balanced nutrition. But such diets can still be high in fat, salt and sugar if this is not controlled carefully.

A healthy diet needs to be combined with regular exercise for people to be able to reap further health benefits, as well as avoiding smoking and only consuming alcohol at or below nationally recommended levels.

Overall, this review does not appear to conclusively prove that a vegetarian or vegan diet is better for a person with type 2 diabetes. It certainly provides no evidence that this diet cures diabetes, as one of the news headlines suggests.

Provided you do your homework, it is possible to eat healthily on a vegetarian or vegan diet. But if you do have type 2 diabetes, we recommend that you talk to the doctor in charge of your care before making any radical changes to your diet. 

Analysis by Bazian. Edited by NHS Choices.
Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Links To The Headlines

Vegetable diet WILL beat diabetes: Meat-free lifestyle cures killer disease, experts claim. Daily Express, November 24 2014

How becoming a vegetarian can CURE diabetes: Plant-based diets improve blood sugar levels, scientists claim. Mail Online, November 24 2014

Links To Science

Yokoyama Y, Barnard ND, Levin SM, Watanabe M. Vegetarian diets and glycemic control in diabetes: a systematic review and meta-analysis. Cardiovascular Diagnosis and Therapy. Published online October 10 2014

Categories: NHS Choices

Pages