Low-carb, high fat diet advice questioned
Low-carb, high fat diet advice questioned
- Expert reaction
25 May 2016
Experts are questioning the findings of a new report from UK health charities that has called for an overhaul of dietary guidelines.
The report, titled Eat Fat, Cut The Carbs and Avoid Snacking To Reverse Obesity and Type 2 Diabetes, was published by the Public Health Collaboration and the National Obesity Foundation, two UK-based charities.
Citing a number of studies, the
authors conclude that a low-carbohydrate, high-fat diet of
real foods is an "acceptable, effective and safe approach"
to weight loss and health.
The Science Media Centre gathered the following expert commentary on the report.
Prof Jim Mann, Professor of Nutrition, University of Otago, comments:
"'Eat fat and cut the carbs to reverse obesity and type 2 diabetes' - Such a statement which questions conventional wisdom and relates to a critically important health issue is bound to attract attention. This is the title on a Report which comes up with 10 key points, the first two being particularly controversial:
• Eating fat doesn’t make you fat
• Saturated fat doesn’t cause heart disease
"These suggestions are not new. Does this report, which comes from a group called The National Obesity Forum, provide confirmation? One should always be open to new information but I would suggest that this report contributes little.
"The Forum comprises a group of self-selected individuals most of whom have repeatedly expressed similar views in the lay and health-related media for many years. They do not represent any recognized professional group and most have not themselves undertaken relevant research. The report itself is not peer reviewed.
"The report is largely based on selective quotations from the relevant literature. There are many mistakes but the reference (or failure to refer) to the relevant papers commissioned by the Nutrition Guidance Advisory Group of the WHO serves as a good example.
"The report quotes one of the papers by De Souza et al ‘saturated fat intake was not associated with all-cause mortality, CVD mortality, total CHD, ischaemic stroke, or type 2 diabetes’. However it does not mention the limitations which the authors discuss, nor does it quote the two other studies which may help to inform WHO opinion and which demonstrated (a) that those who choose to restrict their total fat intake tend to have a lower body weight and (b) that replacement of saturated fat with unsaturated fat in randomised controlled clinical trials is associated with a reduced risk of coronary heart disease events.
"All these studies were based on meta-analyses which aggregate the results of all available appropriate studies and were published in world leading peer reviewed journals. The report also does not discuss the limitations of the studies used to support the arguments.
"Also missing is a full consideration of the long term trials comparing different nutritional approaches to weight loss. These clearly show that although high fat diets may produce a greater weight loss in the short term, in the longer term the extent of weight loss is dependent on the degree of compliance with the dietary advice regardless of the diet composition, i.e. there is nothing special about high fat diets. People lose weight if they reduce their calorie intake assuming their energy expenditure remains unchanged.
"There are some points in the report which are perfectly reasonable e.g. ‘you can’t outrun a bad diet’ and ‘ industrial vegetable oils should be avoided’ and some which are rather more complex than the Report suggests:
"For example, it is absolutely true that people at risk of type 2 diabetes need to limit starchy and refined carbohydrates but this may not apply across the board and needs further explanation, e.g. in China people are consuming less of their traditional food, i.e. rice and more fat AND they are getting fatter and diabetes rates are increasing dramatically.
"If only life was as simple as the self-styled experts suggest!"
colleagues at the UK SMC collected the following
commentary: Dr Gunter Kuhnle, nutritional scientist at the
University of Reading, comments:
Dr Gunter Kuhnle, nutritional scientist at the University of Reading, comments:
“As with any public health measure, it is important that any recommendations are based on solid evidence, and take the wider implications of implementation into account. That doesn’t seem to be the case in this instance.
“There is only very limited evidence on the long-term impact of using dietary fat as the main source of calories. There are only very few long-term studies, and they do not suggest that cutting back on carbohydrate is as beneficial to health as it is claimed. Virtually no research has been carried out to show the impact of recommending a very low carbohydrate diet to the general public. It could even be very damaging to public health.
“The document presents as fact what has not even achieved consensus in the scientific community, such as the role of fat and carbohydrates, and for which there is only very little evidence. By doing so, it could confuse consumers, and also make discussions within the scientific community and the general public more difficult. In the long term, this is likely to have an adverse effect on public health, as it leads to ‘advice fatigue’.
“Obesity and type 2 diabetes are among the most important health challenges we face. Both conditions put a huge burden on society and the NHS and result in a lot of personal hardship. It is therefore vital that we find ways to prevent and treat these conditions. The call for more evidence-based nutritional advice is very welcome.”
Prof Susan Jebb, Professor of Diet and Population Health at the University of Oxford, comments:
“As the importance of diet as a contributor to ill-health is increasingly recognised, so the evidence has come under greater scrutiny. Nutrition is a complex science, and it’s hard to do classic randomised controlled trials over long enough periods to observe the effects on heart disease or cancer so we need to combine these studies with observational analyses, using new statistical techniques such as Mendelian randomisation to help understand if the associations observed are causal.
“Given this diverse evidence base, dietary guidelines need to be based on comprehensive reviews of the totality of the evidence, assembled and reviewed according to agreed protocols to reduce the chances they may be affected by personal opinion or other biases.
“The new report from the National Obesity Forum fails this standard. It is not a systematic review of all the relevant evidence, and it does not include any assessment of the methodological quality of the studies. The authors are not named and it does not seem to have been peer-reviewed. It should not be confused with other comprehensive reviews of the evidence produced with clear and transparent processes by organisations such as the World Health Organisation or national bodies such as the Scientific Advisory Committee on Nutrition or NICE.
“Instead it ‘cherry-picks’ studies, for example, highlighting one trial suggesting high dairy intake reduced the risk of obesity, while ignoring a systematic review and meta-analysis of 29 trials which concluded that increasing dairy did not reduce the risk of weight gain.”
Prof Tom Sanders, Emeritus Professor of Nutrition and Dietetics at King’s College London, comments:
“This report confuses dietary guidelines for the population with the clinical management of obesity and type 2 diabetes. There is certainly much room for improvement in the clinical management of obesity in the NHS and there clearly is a need for a debate on how best to manage the diet of patients with type 2 diabetes. The medical professional certainly needs to get its act together but it is not helpful to slag off the sensible dietary advice given by Public Health England and the US Dietary Guidelines for Americans.
“Dietary guidelines are designed to ensure an adequate intake of nutrients as well as to prevent dietary related disease. The report wrongly attributes the current obesity/diabetes epidemic to current dietary guidelines. The report fails to recognize that the main driver is our obesogenic environment and insinuates a sinister plot involving collusion between government and the food industry.
“The truth is, most people now live in metropolitan areas, spend much time travelling to and from work and eat much more food outside the home. Food is also more widely available, 24 hours a day, portions sizes are bigger and people are less active because of sedentary occupations (especially sitting in front of a computer) and the increased use of the car.
“The harsh criticism of current dietary guidelines meted out in this report is not justified as few people (~5%) adhere to these guidelines anyway. There is also good evidence that those that do follow the guidelines have less weight gain and better health outcomes.
Dr Mike Knapton, Associate Medical Director at the BHF, comments:
“This report is full of ideas and opinion, however it does not offer the robust and comprehensive review of evidence that would be required for the BHF, as the UK’s largest heart research charity, to take it seriously.
“This country’s obesity epidemic is not caused by poor dietary guidelines; it is that we are not meeting them. Diets that are high in saturated fat have been shown to increase cholesterol. High cholesterol is linked to an increased risk of cardiovascular disease hence why current recommendations emphasise the importance of reducing this.
“Heart disease is a multifactorial condition with a range of risk factors and any dietary and lifestyle advice worth noting should consider the overall impact that our diet and lifestyle has on our health. Focusing on single foods, nutrients or risk factors is short sighted and will perpetuate confusion and fear amongst the public about what they should and shouldn’t eat to protect their heart health.”
Prof Iain Broom, Director of the Centre for Obesity Research and Epidemiology at Robert Gordon University, comments:
“At long last there is some sense coming into dietary advice that may eventually lead to improved health, in particular tacking the double whammy of obesity and Type 2 Diabetes Mellitus. I totally agree with the document produced jointly by the NOF and the Public Health Collaboration, except for the statement re “zero sugar” as all fruits and berries contain sugar – “no added sugar” would be more appropriate.
"At the time of the change in food policy in the USA in the late seventies and in the UK in 1983, there was no evidence to back a reduction in saturated fat in the fight against coronary heart disease, but there was evidence to link CHD to sugar intake.
"A British nutritionist, John Yudkin, at the time tried to prevent such a policy and to shift the blame to sugar and refined carbohydrate, but was pilloried by Ancel Keyes and the establishment. Decades of nutrition students have had to undergo training where this unsubstantiated, and now proven false, link between fat intake and CHD, obesity and diabetes is hammered home.
"We will thus have to undo all of this in the future and to reintroduce the notion that fat in the diet causes neither obesity, T2DM nor CHD."
Prof Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow, comments:
“The report has good, bad and ugly elements in it. Yes, it’s clear that snacking is generally to be avoided; few would argue against this. It’s also clear that some sources of fat will be better than other sources. But to make the headline message that we should all eat more fat as the cure to reverse obesity trends and thus type 2 diabetes is NOT warranted based on the totality of evidence.
“In dietary areas, we have few large scale long term trials and so rely a lot on observational data, the results of which can be interpreted or extrapolated in different ways. Even when we have trials, they are often short term on weight loss alone or some risk factors and cannot give the longer term reality on long term risks or sustainability of diets.
“The authors of this report have been selective in their choice of evidence to support their arguments and there is an abundant literature which goes against their conclusions. Indeed, plentiful evidence supports excessive calories from a variety of sources leading to a rise in obesity with excess fatty foods being a major component of in many individuals.
“Hence, whilst it is good to debate, the report’s main headline – simply to eat more fat - is highly contentious and could have adverse public health consequences.”
Prof Suzanne Dickson, Professor of Neuroendocrinology at the University of Gothenburg in Sweden, comments:
“There are a lot of misleading messages in these guidelines which ultimately do not promote health.
“These new guidelines are not in line with those of the World Health Organization.
“While it may be good to reduce intake of carbohydrates and sugars, there remains a great body of evidence that it is equally important to limit intake of fats. These guidelines make no suggestion on what the upper limit of fat intake should be and without this effectively promote their over-consumption.
“I am not aware of any evidence that common obesity is due to under- or over-production of any hormone.
“I am not aware of any hard evidence that snacking causes obesity. There does exist evidence that snacking causes a compensatory adjustment in caloric intake during the rest of the day. This is not very surprising because energy balance is under tight physiological control.
“It is misleading to suggest that the amount of calories on a plate is ‘irrelevant’.
“Diets fail because food restriction of any kind leads to reduced metabolism coupled with food cravings that eventually overpower restraint.”