Low-carb, high fat diet advice questioned – Expert reaction

 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 lost and health.

Coverage of the report in New Zealand includes:

Stuff.co.nz: “Eat fat” message is “irresponsible” says obesity expert
New Zealand Herald: How to combat obesity: Eat more fat (via Daily Mail)
RadioLive: Eat more fat and less carbs to lose weight

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 The Report itself is not peer reviewed.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 getter fatter and diabetes rates are increasing dramatically.

“If only life was as simple as the self-styled experts suggest!”

Dr Gunter Kuhnle, a nutritional scientist at the University of Reading, said:

“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, said:

On research method:

“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.”

On saturated fat and heart disease

“A central part of the paper is about reducing the risk of heart disease but it starts from a flawed premise.  In the case of heart disease it claims that low HDL and triglycerides are a more important marker than LDL cholesterol. Yet some of the largest trials in the world show that lowering LDL reduces the incidence of heart disease. Moreover there is little evidence that raising HDL is protective either from a trial of a possible drug treatment or Mendelian randomisation studies.

“It is very clear from dietary intervention studies that reducing saturated fat is an effective strategy to reduce LDL and this would be expected to reduce the risk of heart disease. It is true that these trials have not shown reductions in rates of heart disease, but most trials are short-term and people’s ability to maintain a diet low in saturated fat is usually sub-optimal. This suggests people need more support to adopt a diet low in saturated fat; it does not show that such an intervention is unwarranted.”

On diabetes

“The best way to reduce the risk of diabetes is to achieve and maintain a healthy weight.  Large trials show clearly that, for overweight people, even modest weight loss substantially reduces the risk. Losing weight is about reducing calorie intake. Low carbohydrate diets can be an effective way to lose weight because they help cut calories. But while they are labelled as ‘low carb’, cutting carbs generally cuts fat too because there is no butter on bread, oil on pasta etc. It is misleading to suggest that a low carb diet is a license to consume fat in abundance.”

On weight loss

“The report suggests the best advice for weight loss is a low refined carbohydrate diet, eaten without restriction, together with a high healthy fat diet.  There is no evidence from trials that this will help people lose weight. For most people in 21st century Britain, eating freely – even if only from ‘healthy’ foods – is unlikely to lead to spontaneous weight loss. Losing weight requires some control over total energy intake which means limiting some foods, not eating them freely. This is why losing weight is so hard. While calorie-counting isn’t practical for most people most of the time, we do need to be calorie-conscious.”

Prof Tom Sanders, Emeritus Professor of Nutrition and Dietetics at King’s College London, said:

“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.

“The press release as well as the report makes eight potentially harmful statements which in my opinion are likely to mislead the general public.  I’ve listed them below.”

Claim 1: Eating fat does not make you fat

“Their claim that eating fat does not make you fat is absurd and plain wrong.  In the human body fat is almost exclusively derived from dietary fat as there is very little carbohydrate converted into fat.  Drugs or disorders that reduce fat absorption cause weight loss. Eating a lot of carbohydrate with fat increases fat storage.  If you eat a lot of fat you will get fat.”

Claim 2:  Saturated fat does not cause heart disease – Full fat dairy is likely protective

“Many factors are involved in causing heart disease but elevated blood cholesterol is a major contributor to heart disease and lowering blood cholesterol reduces risk. Smoking and high blood pressure increase risk of heart disease especially when cholesterol levels are high.  Saturated fat increases serum cholesterol. Serum cholesterol levels have fallen in countries as saturated fat intakes have fallen because of changes in the food supply (vegetable oils have replaced animal fats and poultry has replaced red meat). Intakes of saturated fat are no longer high in the UK. While some studies show full fat milk and yoghurt not be associated with increased risk of heart disease, it is believed this is due to other nutrients such as calcium and magnesium provided by milk. Butter does increase blood cholesterol more than milk or cheese. Red and processed meat, which are the major sources of saturated fat in the diet are associated with increased risk of heart disease in the prospective studies. Heart disease has fallen substantially in many countries over the past 30 years and there is no evidence to show that the dietary advice given has had an adverse effect.”

Claim 3: Processed food labeled “low fat”, “lite”, “low cholesterol; or “proven to lower cholesterol” should be avoided.

“The report claims ‘Processed food labeled “low fat”, “lite”, “low cholesterol; or “proven to lower cholesterol” should be avoided’.  The term processed food is used carelessly: any food preparation is processing. There is no evidence of harm to justify such statements. The term “proven to lower cholesterol” is only used on some high fibre breakfast cereals (usually oat or barley based cereals) and in spreads containing plant phytosterols.  Phytosterols lower LDL cholesterol by 8-10% and the safety of phytosterols for food was carefully evaluated under the Novel Foods Directive. The health claims regarding lowering cholesterol are subject to the EU Health Claims Regulation and have been carefully evaluated by the European Food Safety Authority”.

Claim 4: Limit starchy or refined carbohydrates to prevent and reverse type 2 diabetes.

“Weight loss and exercise are the only effect dietary measure to prevent diabetes.  There is good evidence from the Finnish Diabetes Prevention Programme that following current dietary guidelines and taking regular exercise reduce risk of diabetes. Dietary measures are less effective in reversing diabetes than bariatric surgery.

“As most food energy comes from carbohydrate, restricting carbohydrate intake can help lower energy intake and promote weight loss. However, there is no benefit if the food energy is replaced by alcohol or fat. Dietary fibre intake is associated with a lower risk of obesity and dietary fibre mainly provided by starchy foods.  Diets based round wholegrains, which are starchy foods, have been shown to be associated with a lower risk of developing type 2 diabetes and are also recommended in the management of type 2 diabetes. “

Claim 5: Optimum sugar consumption for health is zero.

“The report states ‘Optimum sugar consumption for health is zero’. Current dietary advice is to avoid added sugar (in particular sugar sweetened beverages and sweets). There is no evidence to show that reducing added sugar intake below 10% energy has any impact on obesity or type 2 diabetes.  Furthermore, it is not possible to select balanced diets that contain no sugar. All fruit and many vegetables (carrots, beetroot, onions, parsnips, sweet potatoes) contain sugar about 5-10% by weight and milk contains 4-5% sugar. Following the 5-a-day advice for fruit and vegetables and drinking half a pint of milk/day provides about 45 g of sugar. While frequent consumption of sugar contributes to tooth decay, the effects can be minimized by use of fluoride toothpaste and good oral hygiene and avoiding eating sweets.”

Claim 6: Industrial vegetable oils should be avoided.

“The report says ‘Industrial vegetable oils should be avoided’ but it’s clear the term ‘industrial’ is used to indicate a detrimental effect.  Most vegetable oils are refined to remove free fatty acids, gums and mucillages that give rancid flavours.  Refining also makes oils more stable for storage and for cooking. Formerly, some vegetable oils were partially hydrogenated and this resulted in the formation trans fatty acids which later were linked to increased risk of heart disease. Partial hydrogenation is no longer carried out in the UK and this has been the case since 2000. Vegetable oils sold in supermarkets and used in catering are free from trans fatty acids. The only remaining sources of trans fatty acids in the UK diet are butter, beef and lamb fat. The main oils used by consumers are rapeseed, sunflower, olive oil and palm oil. These oils, except for sunflower oil, tend to contain more monounsaturated fatty acids than polyunsaturated fatty acids (the newer varieties of sunflower oil are high in monounsaturated rather than polyunsaturated fatty acids) Corn oil and soyabean oil, which are high in polyunsaturated fatty acids, are not widely used in the UK.  Intakes of polyunsaturated fatty acids have been quite stable in the UK food supply for the last 20 years and account for 5-6% of the dietary energy. Generally, it is sensible to limit intake because adding fat to food is fattening. As guidance no more than a tablespoonful a day (15ml) is recommended.

“In the USA there is good evidence to show that vegetable oil consumption has increased from about 15g in the 1970s to 45g/day nowadays.  In my view, there is little doubt that a high consumption of deep-fried food contributes to obesity as the film Supersize Me clearly demonstrated.”

Claim 7: Stop counting calories.

“Weight is only gained when calorie intake exceeds calorie expenditure. Calorie labeling is useful for consumers. All dietary advice that results in reduced calorie intake results in weight loss. Many obese individuals have difficult in maintaining long-term reductions in calorie intake because of the appetite drive that makes them want to reach their “set point” for weight.

“The report says that calorie focused thinking has damaged public health.  This is not true. In a world where most food is either consumed outside the home or ready prepared, calorie labeling helps consumed make healthier choices.  Many consumers choose not read food labels, especially those in low socioeconomic groups. The evidence is that high socioeconomic status is a associated with a lower prevalence of obesity and the more educated and better off people are the more likely they are to read food labels.

“There remains a pressing need for individuals to be made aware of how much food energy they need.  My lifelong experience of over forty years working as a nutritionist shows me than people who balance calorie intake with expenditure maintain a stable weight.”

Claim 8:  You cannot outrun a bad diet

“Regular exercise can help prevent weight gain.  Brisk walking daily also reduce risk of type 2 diabetes independent of any weight loss.  Exercise, however, is not an effective means of losing weight but when combined with calorie restriction can help prevent loss of muscle tissue and reduce fatty liver. This report muddles quality and quantity because you can still eat too much of a “good diet”.  Obesity is caused by eating too much – not just by eating unhealthy foods”.

Dr Mike Knapton, Associate Medical Director at the BHF, said:

“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, said:

“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.

“In terms of coronary risk it is well known that the most atherogenic plasma lipid profile is a low HDL cholesterol with raised triglycerides and that high carbohydrate intake is linked to such a profile.  In addition the plasma lipid abnormality associated with T2DM is low HDL and raised triglycerides, not a raised cholesterol or raised LDL cholesterol.  It is thus illogical to suggest that the most appropriate diets for patients with T2DM are ones based on high carbohydrate intake as this is even more likely to increase the risk of atherogenic disease in these patients.  T2DM patients are, by definition, insulin resistant, but the insulin resistance is different between fat tissue and lean tissue, the receptor on the fat tissue being much less resistant, and hence a diet rich in carbohydrate will, by necessity, drive up insulin values resulting in net fat deposition.  This is one reason why patients with T2DM, and for that matter patients with polycystic ovary syndrome, another insulin resistant pathology, find weight loss difficult when all treatment is based on high carbohydrate intakes.  I have long treated patients with T2DM using a low carbohydrate approach and successfully removed some of these patients from being insulin requiring or using insulogenic drugs.  Presenting this data at Diabetes UK meetings or Heart UK meetings has, in the past, frequently been met with attempted ridicule.

“Not only has Brazil adopted a much reduced carbohydrate content of their advised ‘healthy diet’, but a scientific committee in Sweden in 2013 recommended a reduction in carbohydrate intake in the diet to between 26 – 40% of energy intake, from the current recommended intake of >50% of energy intake, with a corresponding increase in fat, including saturated fat.  Here in the UK the members of SACN, a number of whom have links with the food industry, have continuously failed to take note of the accumulating evidence in favour of introducing higher fat intakes, including saturated fat despite the evidence.  The FDA in the USA have also continued along their longstanding theme re fat.  I presume such individuals in the UK and USA would still be telling us the world is flat and not round, and that you would fall off the end if you went to far N, S E or W.

“The continuation of a food policy recommending high carbohydrate, low fat, low calorie intakes as ‘healthy eating’ is fatally flawed.  In terms of obesity and T2DM this is a failed strategy, and this may also be the case for cancer.  Our populations for almost 40 years, have been subjected to an uncontrolled global experiment that has gone drastically wrong.  It is now time for Governments to grasp the nettle and admit they and their scientific advisors have got it wrong and attempt to repair the damage, but without destroying public confidence.  Granny’s recommendation for good wholesome food is appropriate, the current food industry’s preoccupation with pre-prepared and processed food is inappropriate.”

Prof Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow, said:

“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, said:

“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.

The UK SMC produced a Factsheet / Briefing Note on sugar and health which is available here: http://www.sciencemediacentre.org/sugar-and-health/

Declared interests

Prof Sattar was senior author on a trial which was funded by Coca-Cola on a placebo-controlled RCT of a novel flavonoid rich beverage – the trial was negative

Prof Sanders is a Scientific Governor of the charity British Nutrition Foundation, member of the scientific advisory committee of the Natural Hydration Council (which promotes the drinking of water), and honorary Nutritional Director of the charity HEART UK. Prof. Tom Sanders is now emeritus but when he was doing research at King’s College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks. In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011. This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof. Hough at the Queen Elizabeth College (QEC), which merged with King’s College London. The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar. Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006. Tom also used to work for Ajinomoto on aspartame about 8 years ago.  Tom was a member of the FAO/WHO Joint Expert Committee that recommended that trans fatty acids be removed from the human food chain. Tom has previously acted as a member of the Global Dairy Platform Scientific Advisory Panel and Tom is a member of the Programme Advisory Committee of the Malaysian Palm Oil Board. In the past Tom has acted as a consultant to Archer Daniel Midland Company and received honoraria for meetings sponsored by Unilever PLC. Tom’s research on fats was funded by Public Health England/Food Standards Agency.

Prof Susan Jebb is employed by the University of Oxford and receives no personal funding from the food industry.  Susan Jebb is conducting research into the treatment of obesity, some of which include support from WeightWatchers, Slimming World and the Cambridge Weight Plan.  Susan was the independent Chair of the Public Health Responsibility Deal Food Network and was a science advisor to the Foresight obesity report. From 2007-10 she was the principal investigator for a research study funded by the food industry to investigate the potential for a functional beverage to help weight loss. The results of this work have been published: http://www.ncbi.nlm.nih.gov/pubmed/23920353

Dr Gunter Kuhnle: I was involved in research funded by the Medical Research Council and World Cancer Research Fund looking at links between sugar and obesity.  I am also funded through the European Union and industry to investigate the health effects of flavanols and other plant compounds.