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expert reaction to study investigating low-fat diets, compared to other diets, and long-term weight loss

The effect of the nutrient content of a diet on its impact on long-term (more than one year) weight loss is the subject of a paper published in The Lancet Diabetes & Endocrinology, in which the authors report that “low-carbohydrate” diets led to greater weight loss than “low-fat” diets.


Tracy Parker, BHF (British Heart Foundation) Heart Health Dietitian, said:

“Identifying what diet is best for losing weight has been widely debated for years, especially with the increasing prevalence of obesity.

“This systematic review and meta-analysis of randomised controlled trials compared the effects of low fat and higher fat dietary interventions on long term weight loss. Results from the review suggest that low fat dietary interventions do not lead to greater weight loss than other higher fat dietary interventions, concluding that there is no good evidence for recommending low-fat diets.

“Results showed that when low fat weight loss interventions were compared with other higher fat weight loss interventions, the long term weight loss was just 0.36kg, whilst the low carbohydrate, higher fat weight loss diets led to an average weight loss of 1.15kg.  However, when comparing groups following their usual diet, the low fat weight loss intervention led to a 5.4kg greater weight loss.

“But there was significant heterogeneity between the studies being compared, which the author did recognise, suggesting inconsistent effects across the studies. There were various intervention designs with the low fat interventions varying from very low fat diet with less than 10% of calories coming from fat to 30% of calories from fat; the intensities of the interventions varied from pamphlets to multicomponent programmes and there was considerable drop out or adherence to the diets and loss to follow up in most of the trials.

“When it comes to weight loss, the primary goal continues to be achieving an energy deficit – using up more than we take in. However, there are a multitude of ways that we can do this. Whether you choose a low fat, low carbohydrate or high protein diet, the important things are that you stick to it and that it doesn’t leave you lacking in nutrients required for general health. There are no quick fixes, changing our eating habits and lifestyles can be a challenge and take time to do. Losing weight and keeping it off for good is all about following a sustainable plan – making small, achievable changes to diet and activity levels will make a big difference in the long term.”


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

“I think the message of this paper is that all diets work but to a modest extent with little difference between different types of diets over the first year in terms of weight loss. What this study cannot show is what the adherence to diets were after several years and in reality, individuals will return to some sort of habitual diet. We need more work on sustaining weight loss. The results also indirectly suggest more emphasis should be placed on helping individuals stopping becoming obese in first place, and for this area we need specific trials and input (currently absent) from the government and food industry to alter food formulations, consider taxes etc., so that individuals are more easily directed to better food choices.”


Prof. Susan Jebb, Professor of Diet and Population Health, University of Oxford, said:

“This study, which has systematically reviewed data from all the relevant trials, reinforces the evidence from individual studies that dieting, whether low fat or low carbohydrate, works. Unfortunately the headline to the press release, ‘low-fat diets ineffective for achieving long-term weight loss’, is totally misleading. In the analysis of trials aimed at weight loss, low fat diets compared to no dieting led to a reduction in weight of 5.4 kg (12lb) after at least 1 year while low carbohydrate diets were associated with, on average, an additional 1.15 kg greater weight loss than low fat diets.

“Weight losses of 5 kg may be less than many people might hope for but we know from many other research studies that this brings surprisingly large health benefits; more than halving the risk of developing diabetes in people with raised blood sugar. These benefits are attenuated but not lost if weight is regained. Inaccurate reports that dieting is “ineffective” undermine public confidence and deter health professionals from encouraging and supporting people who are overweight to lose weight. Yet treating obesity is one of the best investments we can make to improve public health.”


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

“This study has been carried out by a competent and experienced group.  Intakes of fat in the Western world now supply on average 30-35% energy (1); this study defined low fat diets as those containing less than 30% of the energy, which is barely different from usual intakes.

“The data show no major differences in weight loss for calorie restricted low fat interventions compared with comparator interventions supplying higher amounts of fat but similar energy intakes. It is not surprising that the diets focusing on restricting carbohydrate intake led to slightly greater weight loss (by ~1kg), as carbohydrate typically supplies 45-50% of the energy intake. It is easier to reduce energy intake by cutting back on the amount of bread, potatoes and rice in the diet.

“An assumption made in this analysis is that the participants achieved the targets set. However, many, if not most, dietary studies fail because participants fail to follow the dietary advice. For example, in the Women’s Health Initiative Trial (2), which is the largest trial, few women met the 20% energy from fat target, but those who did substantially report a reduced fat intake did lose more weight. In that trial, the 19,541 women randomised to the low fat diet lost 2.2 kg compared to the 29,294 women randomised to the control intervention in the first year, but after 7.5 years the difference between groups was only 0.4 kg, which would suggest that in the longer term they did not comply with dietary advice or they made other changes in their diet.

“To me the take home message from this paper is that energy intake determines the extent of weight loss rather than the relative proportions of fat and carbohydrate in the diet. However, it is the absolute intakes of fat and carbohydrate that determine energy intake. In order to control body weight, it still remains sensible advice to eat less (restrict portion size) and avoid consuming excess amounts of fat and sugar especially as fatty meat, deep fried foods, cakes and biscuits and sugar-sweetened beverages.”

1)   Harika, RK, Eilander, A, Alssema, M, Osendarp, SJ & Zock, PL (2013). Intake of Fatty Acids in General Populations Worldwide Does Not Meet Dietary Recommendations to Prevent Coronary Heart Disease: A Systematic Review of Data from 40 Countries. Ann Nutr Metab 63, 229-38.

2)   Howard, BV, Manson, JE, Stefanick, ML, Beresford, SA, Frank, G, Jones, B, Rodabough, RJ, Snetselaar, L, Thomson, C, Tinker, L, et al. (2006). Low-Fat Dietary Pattern and Weight Change over 7 Years: The Women’s Health Initiative Dietary Modification Trial. JAMA 295, 39-49


‘Effect of low-fat diet interventions versus other diet interventions on long-term weight change in adults: a systematic review and meta-analysis’ by Deirdre K Tobias et al. published in the Lancet Diabetes & Endocrinology on Friday 30 October 2015. 


Declared interests

Prof. Naveed Sattar declares that he has no relevant interests.

Prof. Susan Jebb: “My institution has received research support, either funding or in kind from the Cambridge Weight Plan, Weight Watchers and Slimming World who provide weight management services.”

Prof. Tom Sanders: Prof Tom Sanders 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.  Tom is also 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. Tom 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.

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