New Low Fat versus Low Carb Diet Study – when a tie is not a win

A new one-year study from Stanford University[1] was released February 20, 2018 and reports that low carb diets are no better than low fat diets for losing weight. On one hand, such a conclusion seems like progress when the debate used to be whether low carb diets were “dangerous” – now it’s whether low fat diets are as good as low carb diets.

The conclusion that there was no significant difference in weight loss between a low fat diet and a low carbohydrate diet sounds good on the surface, however closer examination of the methodology indicates that the ‘low carb’ intervention group was only low carb  (≤ 20 g of carbs per day) for the first 8 weeks of a the one year study. After that subjects were instructed to “add carbs back in until they reached the lowest level they believed they could maintain indefinitely. This resulted in subjects in the ‘low carb group’ eating ~100 g carbs per day at 3 months and at the end of the study were averaging 130 g carbs per day ; hardly a ‘low carb’ diet!

The American Diabetes Association (ADA) in its Clinical Practice Recommendations [3] and  Standards of Medical Care in Diabetes [4]  already approves of a 130 g / day intake of carbohydrate as a weight-loss option for those with Type 2 Diabetes in what it calls a low carbohydrate’ diet (more in this article).

The ‘low fat‘ intervention group in this study ate an almost equivalent amount of fat and carbohydrate (48% carbohydrate and 29% fat) as the standard ‘low fat diet’ recommendation of the American Diabetes Association, so the fact that they didn’t find a difference between the two groups should come as no surprise, given that the ADA has already concluded that both are equally effective for weight loss (see quotations below).

Keep in mind when you read the quotes below, what the American Diabetes Association defines as "a low carbohydrate diet" is 130 g carbohydrate per day, which is the same as the average intake of carbohydrates at a year in this study.  

The amount of 130 g carbs per day is a moderate-low carbohydrate diet when compared with the the intake of the first 8 weeks in the study (≤ 20 g carbs / day) and in light of the fact that the average adult US intake is almost 300 g carbs per day.

“The evidence is clear that both low-carbohydrate* [i.e. moderate low carbohydrate] and low-fat calorie restricted diets result in similar weight loss at one year. We’re not endorsing either of these weight-loss plans over any other method of losing weight.  What we want health care providers to know is that it’s important for patients to choose a plan that works for them, and that the health care team support their patients’ weight loss efforts and provide appropriate monitoring of patients’ health.”

– Dr. Ann Albright, RD, President, Health Care & Education, American Diabetes Association, Clinical Practice Recommendations [3]

“For weight loss, either low-carbohydrate* [i.e. moderate low carbohydrate] or low-fat calorie-restricted diets may be effective in the short-term (up to 1 year).”

– Summary of 

In actuality, this “new study” didn’t find anything “new”.

Both the ‘low fat’ and ‘low carb’ [i.e. moderate low carb] groups were instructed to “avoid sugar and refined carbohydrates” but the absolute level of carbohydrate in the ‘low fat’ diet group was not held constant. The
‘low fat’ group actually lowered its carbohydrate intake over the course of the year-long study – from ~242 g carbohydrate per day at the beginning to between 205 g and 213 g carbohydrate per day. This means that the difference  between the two study groups when it came to the level of carbohydrate was decreasing. No wonder there was no significant difference found.

DIETFITS – carbohydrate intake between groups

Final thoughts…

This was not really a study between a ‘low carbohydrate’ diet and a ‘low fat’ diet with fixed grams per day of carbohydrates in each group. This was a study between a flexible moderate carbohydrate diet and a flexible moderately-low carbohydrate diet.

In fact, this “new study” ended up comparing the two diets that have already been approved by the American Diabetes Association and which the ADA has already concluded that neither is more effective than the other for weight loss.

Hardly new.

If you would like to read well-researched, credible “Science Made Simple”  articles on the use of a low carb or ketogenic diet for weight loss, as well as to significantly improve and even reverse the symptoms of Type 2 Diabetes, high cholesterol and other metabolic-related symptoms, please  click here.

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  1. Gardner CD, Trepanowski JF, Del Gobbo LC, Hauser ME, Rigdon J, Ioannidis JPA, Desai M, King AC. Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion – The DIETFITS Randomized Clinical TrialJAMA. 2018;319(7):667–679.
  2. American Diabetes Association, Adjusting the Meal Plan,
  3. Dairman T., Diabetes Self-Management, ADA’s New Guidelines OK Low-Carb Diets for Weight Loss, 2008 Jan 7,

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Author: Joy Kiddie, MSc, RD

Joy Y Kiddie MSc., RD - I'm a Registered Dietitian in private practice in British Columbia, Canada that provides low carb and ketogenic services in-person in my Coquitlam office, as well as by Distance Consultation (using Skype / telephone).