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Handful of nuts 'cuts heart disease and cancer' risk

NHS Choices - Behind the Headlines -

"People consuming at least 20 grams of nuts daily less likely to develop potentially fatal conditions such as heart disease and cancer," The Independent reports. That was the main finding of a review looking at 20 previous studies on the benefits of nuts.

Researchers found consistent evidence that a 28 gram daily serving of nuts – which is literally a handful (for most nuts) – was linked with around 20% reduced risk of heart disease, cancer and death from any cause.

However, as is so often the case with studies into diet and health, the researchers cannot prove nuts are the sole cause of these outcomes.

It's hard to discount the possibility that nuts could be just one component of a healthier lifestyle pattern, including balanced diet and regular physical activity. It could be this overall picture that is reducing risk, not just nuts.

The researchers tried to account for these types of variables, but such accounting is always going to be an exercise in educated guesswork.

Also, many non-lifestyle factors may be involved in any individual's risk of disease. For example, if you are a male with a family history of heart disease, a healthy diet including nuts can help, but still may not be able to eliminate the risk entirely.

The link between nuts and improved health is nevertheless plausible. As we pointed out during a discussion of a similar study in 2015: "Nuts are a good source of healthy unsaturated fats, protein, and a range of vitamins and minerals … Unsalted nuts are the healthiest option."

 

Where did the story come from?

The study was carried out by researchers from Norwegian University of Science and Technology, Trondheim, Norway, Imperial College London, and other institutions in the US.

It was funded by Olav og Gerd Meidel Raagholt's Stiftelse for Medisinsk forskning (a Norwegian charitable foundation), the Liaison Committee between the Central Norway Regional Health Authority and the Norwegian University of Science and Technology (NTNU), and Imperial College National Institute of Health Research (NIHR) Biomedical Research Centre (BRC).

The study was published in the peer reviewed medical journal BMC Medicine on an open-access basis, so it is free to read online.

The UK media presents the results reliably but without discussing the inherent potential limitations of the type of observational evidence examined by the researchers.

 

What kind of research was this?

This was a systematic review that aimed to examine the link between nut consumption and risk of cardiovascular disease, cancer and death.

Previous studies have suggested an intake of nuts is beneficial, and some have found it could be linked with reduced risk of cardiovascular disease and cancer. Other studies though have found no link. The researchers consider the possibility that there is a weak link and that's what they aimed to look at.

A systematic review is the best way of compiling all literature on a topic available to date. However, systematic reviews are only as good as the underlying evidence. Studies looking at dietary factors are often observational and it is difficult to rule out the possibility of confounding variables from other health and lifestyle factors.

 

What did the researchers do?

The researchers searched two literature databases to identify any randomised controlled trials (RCTs) or prospective cohort studies that had looked at how nut intake in adults was linked with cardiovascular disease, cancer and death from any cause.

Studies had to report information on nut intake specifically (ideally by dose and frequency). Researchers assessed the quality of studies for inclusion.

Twenty prospective cohort studies met the inclusion criteria. Nine studies came from the US, six from Europe, four from Asia, and one came from Australia. All studies included adult populations; five were in women only, three in men only, and 12 in a mixed population.

The researchers did not find any suitable RCTs to include in their analysis. This is not especially surprising as RCTs involving diet are notoriously difficult to carry out. You could never be sure that everyone who was randomised into the "eat no nuts" group would stick to the plan, or vice versa.

Also they'd need large samples and long follow-up times to capture disease outcomes, so are not usually feasible. 

 

What did they find? Cardiovascular disease

Twelve studies (376,228 adults) found nut consumption reduced the risk of cardiovascular disease. Each 28 gram/day serving was linked with a 21% reduced risk of cardiovascular disease (relative risk [RR] 0.79, 95% confidence interval [CI] 0.70 to 0.88).

This was for any nut intake, but risk reductions were also found when analysing peanuts or tree nuts separately. Increasing intake was associated with reduced risk up to 15grams/day, above which there was no further risk reduction.

Looking at specific outcomes, 12 studies also found a 29% reduced risk of heart disease specifically (RR 0.71, 95% CI 0.63 to 0.80).

However, 11 studies didn't find a significant link with the outcome of stroke specifically (RR 0.93, 95% CI 0.83 to 1.05).

Cancer

Nine cohorts (304,285 adults) found that one serving of nuts per day reduced risk of any cancer by 15% (RR 0.85, 95% CI 0.76 to 0.94). By separate analysis, the risk reduction was slightly higher for tree nuts (20%) than peanuts (7%).

All-cause death

Fifteen cohorts (819,448 people) recorded 85,870 deaths. One serving of nuts a day was linked with a 22% reduced risk of death during study follow-up (RR 0.78, 95% CI 0.72 to 0.84).

Looking at specific causes of death, each serving of nuts a day was linked with reduced risk of respiratory deaths (0.48 (0.26–0.89); three studies) and diabetes deaths (RR 0.61, 0.43 to 0.88; four studies).

There was no link with deaths from neurodegenerative diseases, and inconsistent links with deaths from kidney disease and infectious diseases. No other disease-related causes were reported.

Overall, the researchers estimate that 4.4 million premature deaths in 2013 across America, Europe, Southeast Asia and Western Pacific could be attributable to nut intakes below 20 grams/day.

 

What did the researchers conclude?

The researchers conclude: "Higher nut intake is associated with reduced risk of cardiovascular disease, total cancer and all-cause mortality, and mortality from respiratory disease, diabetes, and infections."

 

Conclusions

This systematic review finds evidence that nut intake may be linked with reduced risk of cardiovascular disease, cancer and death.

The systematic review has several strengths. It identified a large number of studies with a large total sample size. It also included only prospective cohorts assessing nut consumption and then followed up later disease outcomes.

It excluded cross sectional studies, which assess diet and disease at the same time, and so can't show the direction of effect. It also excluded cohorts that have retrospectively questioned diet when the person already has the disease, which could be subject to recall bias.

However, there are still a number of inherent limitations which mean these studies cannot easily prove that nuts are the magic dietary ingredient that are solely and directly responsible for these outcomes.

There were no randomised controlled trials of nut consumption. All studies were observational where people were choosing their own diet.

The researchers took care to include studies that only looked at nut consumption as an independent factor and looked at results that had adjusted for any confounders. However, the factors that the studies adjusted for, and how well they were assessed, will have varied across studies.

As such it's very difficult to prove that nuts alone are the causative factor and they are not just one component of a generally healthier lifestyle pattern, including balanced diet, regular physical activity, not smoking, and moderating alcohol.

When it comes to frequency or quantity of intake, it is likely there is an element of inaccuracy when people report how much they eat. For example, most people wouldn't weigh out how many nuts they're eating each day.

The review also provides limited information about specific types of nuts. Considering peanuts in particular, the studies included in the review didn't specify whether these are plain nuts, or whether they could have added salt and oils.

It is also likely that cardiovascular and cancer outcomes were not assessed the same way in all studies, for example whether by participant self-report or by checking medical records.

Overall there does seem to be a link between nut consumption and health, but nuts alone won't reduce your risk of cardiovascular disease or cancers, if your lifestyle is still generally unhealthy.

If you want to live a long and healthy life then you should exercise regularly and eat a balanced diet high in fruit and vegetables and low in salt, sugar and saturated fats, while avoiding smoking and moderating your consumption of alcohol.

Nuts are high in "good fats" and can be eaten in moderation as part of a healthy diet. Unsalted nuts are best as excessive amounts of salt can raise your blood pressure.  

Links To The Headlines

Eating handful of nuts a day can keep the doctor away, research proves. The Independent, December 5 2016

Eat nuts every day to cut heart and cancer risk: Just a handful can reduce chance of dying early by a fifth. Daily Mail, December 5 2016

A handful of nuts a day could slash risk of heart disease and cancer. The Daily Telegraph, December 5 2016

Eat a handful of nuts daily to slash your risk of heart disease and cancer. Daily Mirror, December 5 2016

Links To Science

Aune D, Keum N, Giovannucci E, et al. Nut consumption and risk of cardiovascular disease, total cancer, all-cause and cause-specific mortality: a systematic review and dose-response meta-analysis of prospective studies. BMC Medicine. Published online December 5 2016

Could Parkinson's disease start in the gut?

NHS Choices - Behind the Headlines -

"Parkinson's disease 'may start in gut'," BBC News reports. New research involving mice suggests that bacteria in the gut may lead to a greater decline in motor function in patients with Parkinson's disease.

The study involved a mouse model of Parkinson's disease. The researchers gave some of the mice gut bacteria from people with Parkinson's disease, some were given gut bacteria from healthy individuals, and some mice were not given any bacteria.

They found that gut bacteria seemed necessary to trigger Parkinson's-like symptoms. There was greater decrease in motor function in mice infected with gut bacteria compared with those who remained germ-free, with the greatest decline seen in mice given bacteria from people with Parkinson's.

The researchers suggest that the presence of gut bacteria may cause the build-up of proteins called alpha-synuclein, which is found in patients with Parkinson's disease.

The study does not prove that Parkinson's is essentially a gut disorder and could potentially be treated or prevented with antibiotics or probiotics. And, humans aren't identical to mice, so the study findings may not apply to people.

The study arguably raises more questions than answers. But it could pave the way for further studies in people, with the hope of finding potential new treatments for Parkinson's.

 

Where did the story come from?

The study was carried out by researchers from a variety of institutions, mainly from the US and Sweden, including the California Institute of Technology, Rush University Medical Center in Chicago and Chalmers University of Technology in Sweden.

It was funded by the Knut and Alice Wallenberg Foundation and the Swedish Research Council.

The study was published in the peer-reviewed scientific journal Cell. It's available on an open-access basis and is free to read online.

Generally the UK media coverage on this topic was balanced, although the Mail Online did say this study "could overhaul medical research and treatment of Parkinson's" which is possibly over optimistic. 

 

What kind of research was this?

This was an animal study which aimed to investigate a possible link between gut bacteria and brain diseases such as Parkinson's disease.

Parkinson's is a disease of unknown cause where there is a loss of dopamine-producing cells in the brain. This leads to progressive decline in brain and motor function. Typical symptoms include slow movements, stiff muscles and involuntary shaking. There are also often mental health effects such as depression and dementia.

Past evidence has suggested that gut bacteria could influence the development of brain diseases such as Parkinson's by causing build-up of the protein alpha-synuclein (α-synuclein).

However, there was a lack of studies investigating the link through cellular research, an issue the researchers wanted to address.

Animal studies are useful early stage research which can indicate how processes in the body may work. On the other hand, mice and humans are quite different in biology so what works in mice may not necessarily be the same in humans. And even if the findings do apply, they may not provide the whole answer to the causes of diseases such as Parkinson's.

 

What did the research involve?

The research involved two groups of mice aged 12-13 weeks. One group of mice was genetically programmed to produce the protein alpha-synuclein (α-synuclein), which is thought to build up in people with degenerative brain conditions like Parkinson's. Another group of "normal" mice acted as controls.

Within these two groups, the gut composition of the mice was changed. Some mice remained germ-free, some were given gut bacteria from "healthy" donors, and others were given gut bacteria from people with Parkinson's.

The brain and motor function was tested over time in all groups of mice, along with gastrointestinal tests, up to the age of 24-25 weeks. Standardised testing, used for mice, was used to assess motor function.

The test results were compared between the different groups of mice to see whether gut bacteria composition, in combination with the protein, had any effect on the onset of Parkinson-like symptoms.

 

What were the basic results?

Overall, they found that a decrease in motor function for mice with gut microbes compared with those who remained germ-free.

  • The presence of gut bacteria promoted the decline in motor function caused by α-synuclein. Mice genetically modified to produce this protein and then given gut bacteria generally performed the worst in the motor function tests. Gut bacteria from people with Parkinson's caused the greatest decline in motor dysfunction.
  • Mice producing α-synuclein who remained germ-free still showed a decline in motor function by 24-25 weeks old, but the onset was significantly slower compared to the mice with gut bacteria. 
  • The researchers found that gut microbes seemed to be affecting brain function via the action of short-chain fatty acids. The microbes produce short-chain fatty acids. The acids then cause an inflammatory response in the brain's immune cells (microglia) which leads to the dysfunction. 
  • In the germ-free mice there was no fatty acid signalling, limited inflammatory effect and limited motor dysfunction.

 

How did the researchers interpret the results?

The researchers concluded: "remarkably, colonization of aSyn-overexpressing mice with microbiota from [people with Parkinson's] enhances physical impairments compared to microbiota transplants from healthy human donors.

"These findings reveal that gut bacteria regulate movement disorders in mice and suggest that alterations in the human microbiome represent a risk factor for Parkinson's disease."

 

Conclusion

This study aimed to investigate a possible link between gut bacteria and degenerative brain diseases such as Parkinson's.

In the animal model of Parkinson's, researchers found that the presence of gut bacteria seems to enhance the brain's inflammatory response and lead to greater decrease in motor function.

And gut bacteria from people with Parkinson's seemed to have the greatest effect.

But does this mean that Parkinson's is essentially a gut disorder and could potentially be treated or prevented with antibiotics? Unfortunately the answer isn't so simple.

Although these are interesting findings, biological function in mice isn't exactly the same as in humans, so you can't necessarily apply these findings to the human population.

Even if they are applicable in part, this still may not provide the whole answer as to how the disease process of Parkinson's starts. However, it does act as useful early stage research which could pave the way for further studies in humans.

Dr. Arthur Roach, Director of Research and Development at Parkinson's UK commented on this study: "This paper shows for the first time a way in which one of the key players in Parkinson's, the protein alpha-synuclein, may have its actions in the brain modified by gut bacteria. It is important to note however that this study has been done in mice and we would need further studies in other model systems and in humans to confirm that this connection is real … There are still many questions to answer but we hope this will trigger more research that will ultimately revolutionise treatment options for Parkinson's."

Find support in your area for people affected by Parkinson's.

Links To The Headlines

Parkinson's disease 'may start in gut'. BBC News, December 2 2016

Parkinson's could start in the GUT not the brain: Study finds first ever link between the disease and gut microbes. Mail Online, December 1 2016

Links To Science

Sampson TR, Debelius JW, Thorn T, et al. Gut Microbiota Regulate Motor Deficits and Neuroinflammation in a Model of Parkinson’s Disease. Cell. Published online December 1 2016

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