Two Studies Say Low-Fat Diets Don't Work, Amid Wrangling Over Dietary Guidelines

Evidence-Based Diabetes Management, November 2015, Volume 21, Issue SP15

The weeks leading up to the release of the Dietary Guidelines for Americans have seen a series of reports on what kinds of diets work and attacks on the work that went into the report that informs the nation's nutrition policy.

Two meta-analyses of diet studies published within 8 days of each other this fall found that low-fat diets produced less weight loss than those low in carbohydrates. However, interpretations of the analyses differed, offering alternate views on how the results should affect the forthcoming Dietary Guidelines for Americans.

One analysis, appearing October 29, 2015 in Lancet Diabetes & Endocrinology,1 involved 53 studies and more than 68,000 patients, and specifically only included studies of a year or more. Sponsored by the National Institutes of Health (NIH) and the American Diabetes Association, it was accompanied by an editorial, which said that low-fat diets produced less weight loss than low-carbohydrate diets, but neither worked especially well.2 More research was needed, the author wrote, to find out what it would take for Americans to stick with healthy eating plans.

“Participants prescribed low-carbohydrate diets lost only about 1 kg of additional weight after 1 year compared with those advised to consume low-fat diets,” wrote Kevin D. Hall, PhD, of the National Institute of Diabetes and Digestive and Kidney Diseases, in the editorial. (NIDDK is part of the NIH.) “Although statistically significant, such a miniscule difference in weight loss is clinically meaningless.”2

By contrast, a meta-analysis published in PLoSONE October 21, 2015,3 and sponsored by Atkins Nutritionals, was rolled out with a panel discussion at the Four Seasons Hotel in New York City, and a press release with clear conclusions: Low carbohydrate eating deserved equal billing in the nation’s dietary guidelines, even though one of the panelists that day called the exercise a “fool’s errand.”3,4 The panelists that day were advocates of low carbohydrate eating, led by a celebrity moderator, CNN host Lisa Ling.4 The findings, involving 17 trials and 1797 patients, found that low carbohydrate diets produced overall weight loss of an extra 2.0 kg on average along with improved health risks.3

Studies, competing press releases, and hearings before Congress have been the order of the day in the weeks leading up to the release of the 2015 guidelines, which always attract intense interest. But some say this go-around has been especially hard fought, ever since the Dietary Guidelines Advisory Committee (DGAC) released its recommendations in February.

One of the invited guests at the Four Seasons event was Nina Teicholz, author of The Big Fat Surprise, whose critique of the report from the 2015 DGAC report in BMJ became the seminal event in the effort to upend the guidelines. The BMJ article, which was picked up in some media outlets and blasted in others (BMJ issued a clarification)5 hit just ahead of an October 7, 2015, hearing before Congress with Secretaries Tom Vilsack of the Department of Agriculture (USDA), and Sylvia Mathews Burwell of HHS, who oversee the process. A day prior, Vilsack and Burwell announced they would abandon the panel’s recommendation that the 2015 guidelines take sustainability of the food supply into account.6

The big concern of the beef industry has been DGAC’s recommendation that Americans limit consumption of red and processed meat. Lean meat, however, was considered part of a healthy diet, and the panel lifted the longtime recommendation against cholesterol for most people (those whose health conditions require limitations should follow their doctor’s advice). Critics say that despite these changes and more focus on plant-based foods, there is still too much emphasis on carbohydrates. Thus, the DGAC report is also being blasted by the Sugar Association over a separate recommendation for daily added sugar limits.4

That’s not to say that the Dietary Guidelines have not had flaws over the decades. In an interview with Evidence-Based Diabetes Management, Osama Hamdy, MD, PhD, of the Joslin Diabetes Center, said the old food pyramid that once dominated nutritional thinking did a lot of damage. But Hamdy said de-emphasizing carbs doesn’t mean a diet with lots of bacon or saturated fats is a great idea, either. The Why WAIT diet he developed for a weight-loss intervention limited saturated fat to 10% of the diet and carbohydrates to 40%.7

In 2011, nutrition policy made a significant change at the consumer level with “My Plate,” which puts less emphasis on carbohydrates; recommendations that had emphasized multiple servings of breads and cereals now said “make half your plate fruits and vegetables.” On a parallel track, the FDA has been moving toward new food labels that do more to highlight added sugars, in response to criticisms that Americans backfilled fats with sugar to replace the calories.8

References

1. Tobias DK, Chen M, Manson JE, Ludwig DS, Willett W, Hu FB. Effect of low-fat diet interventions versus other diet interventions long-term weight change in adults: a systematic review and meta-analysis [published online October 30, 2015]. Lancet Diab Endocrinol. 2015; doi:10.1016/S2213-8587(15)00367-8.

2. Hall KD. Prescribing low-fat diets: useless for long-term weight loss? [published online October 30, 2015]. Lancet Diab Endocrinol. 2015; doi:10.1016/S2213-9597(15)00413-1.

3. Sackner-Bernstein J, Kanter D, Kaul S. Dietary intervention for overweight and obese adults: comparison of low-carbohydrate and low-fat diets. A meta-analysis. PloS ONE. 2015;10(10):e0139817. doi:10.1371/journal.pone.0139817.

4. Caffrey MK. The low-carb study was straightforward. Then somebody called the Dietary Guidelines a “fool’s errand.” The American Journal of Managed Care website. http://www.ajmc.com/focus-of-the-week/1015/the-low-carb-study--was-straightforward-then-someone-called-the-dietary-guidelines-a-fools-errand. Published October 22, 2015. Accessed November 5, 2015.

5. Teicholz N. The scientific report guiding the US dietary guidelines: is it scientific? [published online September 23, 2015]. BMJ. 2015;351:h4962. doi:10.1136/bmj.h4962.

6. Vilsack T, Burwell SM. 2015 Dietary Guidelines giving you the tools you need to make healthy choices. USDA website. http://blogs.usda.gov/2015/10/06/2015-dietary-guidelines-giving-you-the-tools-you-need-to-make-healthy-choices/. Published October 6, 2015. Accessed November 5, 2015.

7. Smith A. Joslin’s Hamdy: Evidence shows diet, exercise effective against diabetes, obesity long-term. Am J Manag Care. 2015;21(SP13):SP453-SP454.

8. Bourg M. Food industry discusses DGAC call for sugar limits, but many are cutting back already. Am J Manag Care. 2015;21(SP13):SP450.