Comparing low-fat and low-carb diets finds little difference

By Dr. Ananya Mandal, MDFeb 22 2018

Researchers have studied the effects of a low fat versus and low carbohydrate diet over one year in overweight and obese individuals and come up with some insights into their genetic makeup as well as responses to these diets.

The study titled, “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 Trial” was published in the latest issue of the journal JAMA.

Dr. Christopher D. Gardner and his team looked into the age old question of which was better – a healthy low fat diet (HLF diet) or a health low carbohydrate diet (HLC). They looked at the effects of these diets over one year on obese and overweight individuals and also looked for any genetic connection and relation these could have on insulin resistance. Insulin is a hormone that helps the body utilize the dietary glucose or sugars. Insulin resistance is a condition where the amount of insulin produced by the body fails to meet the demands. This is a common occurrence in persons with type 2 diabetes mellitus. Earlier studies have shown that diet and insulin resistance is intimately linked. Diet changes have been advocated for weight loss and reduction of diabetes risk but the exact extent of benefits from low fat or low carbohydrate diets have not been compared head one before this.

This was a clinical trial named “The Diet Intervention Examining The Factors Interacting with Treatment Success (DIETFITS)” involving 609 overweight adults aged between 18 and 50 years whose body weight change was observed over 12 months. The Body mass index or BMI of the participants ranged between 28 and 40. Three genes were checked along with pattern of insulin secretion that could help assess presence of insulin resistance. Among the participants, 305 were given HLF diet while 304 participants were given HLC diets. These were incorporated in 22 diet counselling sessions to reduce 500 to 600 calorie intake per day. At the start of the study, 40 percent of the participants had a low fat genotype and 30 percent had a low carbohydrate genotype. Average insulin secretion at baseline or INS-30 was 93 μIU/mL.

Results showed that HLF diet could help reduce an average of 5.3 Kg while HLC diet could help reduce around 6 kg over the 12 month period. This showed that there was no major difference in either of these diets as a whole. All of the participants were assessed genotypically and their insulin resistance was checked at the beginning of the study. Results revealed neither genetic makeup nor insulin resistance at the start of the study could predict or affect the weight loss with either types of diet. Blood cholesterol including LDL cholesterol was significantly lowered in the HLF diet but triglycerides were lowered in both groups. HDL cholesterol or good cholesterol was raised in the HLC diet group only.

Authors concluded that “there was no significant difference in weight change between a healthy low-fat diet vs a healthy low-carbohydrate diet, and neither genotype pattern nor baseline insulin secretion was associated with the dietary effects on weight loss.” This meant that both diets were equally effective for weight loss.