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Low-Fat vs. Low-Carbohydrate Diet: Which is Better?

fruit and vegetables

A new study has shown that it isn?t so much the type of diet, Low-Fat vs. Low Carb, but a more a matter of quality of the diet! A Stanford University study published in the Journal of the American Medical Association, has concluded that both diets can work equally well at shedding unwanted pounds as long as people consume healthy vegetables and whole foods and cutting back on refined grains, sugar and highly processed foods. And of course people have to stick to the diet!

Christopher Gardner, Director of Nutrition Studies at the Stanford Prevention Research Center, states they found no evidence that a person?s genotype (genetic makeup) or the individual way their body responds to insulin determines which diet type most likely to help them with their weight loss. Past research has indicated that genetic and insulin levels might explain why some people lost more weight on a low-carb diet vs. a low-fat diet or vice versa. The Stanford colleagues decided to study those assumptions by conducting a randomized clinical trial which is considered the gold standard for testing hypothesis.

The researchers recruited 609 adults aged 18 to 50 and evenly divided between men and women. All had a body mass index of between 28 and 40. All underwent a variety of tests at the beginning of the study including one test that looked for genetic variants linked to the metabolism of fasts and carbohydrates and one that measured the body?s response to insulin.

Participants were randomly assigned to either a low-carb diet or a low-fat diet which they were to follow for one year. Those on the low-fat diet were encouraged to cut down to 20 grams of fat per day for the first eight weeks of the study. Those in the low-carb group were asked to cut down to 20 grams of carbs per day. These were fairly large changes from what they had a their baselines.

During the first two months they were told they could add back small, incremental amount of carbs and fats until they reached a level they felt they could successfully maintain for the rest of their lives. At the end of the year study, those on the low-fat diet averaged 57 grams of fat daily and those on the low-carb diet were averaging 132 grams of carbohydrates daily which is much lower than the 83 grams of fat and 247 grams of carbs the groups were averaging at the beginning of the study.

During the study the groups were counseled on how to eat a healthy low-carb or low-fat diet. The main point was eating quality including buying fresh food and produce at the Farmer?s Market, cooking more yourself, eating with others, and watching snacking habits. They were also told to eat very little refined grains and sugar and focus on eating a lot of vegetables. And they were told to eat so that they didn?t feel deprived or hungry.

The main findings showed that the weight loss at the end of the year for both groups was very similar ? an average of 11 pound loss for the low-fat group and an average of just over 13 pounds for the low-carb group. The data also showed that people with genetic variations linked to a low-fat diet response were not more likely to lose weight on a low-fat diet nor were people with genetic variations linked to a low-carb diet response were likely to lose weight on a low-carb diet. Additionally, those with a poor insulin response were not more likely to lose weight on a low-carb diet vs. a low-fat diet. This proved the researchers original hypotheses true.

The study did have some limits. The participants tended to have higher levels of education that the general public and resources that enabled them access to high quality food. And the participants were only followed for one year. The studies findings do offer the best evidence to date for how low-fat and low-carb diets compare when it comes to weight loss and genetic factors.

Reference: 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 SecretionThe DIETFITS Randomized Clinical Trial. JAMA. 2018;319(7):667?679. doi:10.1001/jama.2018.0245