31 . 05 . 2018

Low Fat vs. Low Carb Diet - 12 month study

Nowadays there is an intense debate about the most effective weight loss strategy. On one side, the low carbohydrate diet fans attribute the obesity epidemic to carbohydrate consumption. In opposition, the low fat advocates, establish a direct association between fat intake and fat deposition in our bodies.

Earlier this year, a group of researchers of the Stanford University published a study on this topic, called DIETFITS (“Dietary Intervention Examining The Factors Interacting with Treatment Success). In this study, 609 overweight people were randomized to two different groups and followed different diets for 12 months: a low carb diet (LC) vs. a low fat diet (LF).

The initial cohort had an average age of 40 years old, average BMI of 33 and was composed of 57% women.

There were multiple instructional sessions led by nutritionists and educators that assisted on diet implementation. The team of researchers was extremely careful in recommending healthy diet principles for both groups. Consumption of vegetables was encouraged, in detriment of refined grains, industrial seed oils and processed foods.

Individual diets were adjusted, so that people could adhere to them and didn’t drop out of the study. For the LF group, in average, the macronutrient ratio was: 20% protein, 30% fats and 50% carbohydrates. For the LC group, in average, the energy was supplied by: 23% protein, 47% fats and 30% carbohydrates.

After 12 months, 479 people (241 in the LF group and 238 in the LC group) finished the study.

There was no statistically significant difference in weight loss between the 2 groups:

  • Average weight loss of 5.3 kg in the LF group
  • Average weight loss of 6.0 kg in the LC group

There are several other important points, worth mentioning, in this study:

  • Neither of the diets had an extremely restrictive macronutrient distribution and both are perfectly sustainable.
  • In both groups there was a calorie intake decrease of, approximately, 500 calories even though there was no indication to count or restrict calories. Maybe the major advantage of these strategies is calorie restriction.
  • In each of the groups there was a large range of weight change among participants. Some people gained 10 Kg during the study, while others lost 30 Kg. Maybe the people that gained weight on a diet, would have lost weight on the “opposite” approach?
  • The investigators used genetic polymorphism testing (3 genes – PPARG, ADRB2 and FABP2) that, supposedly, determine genotypes more prone to lose weight on a low carb or low fat diet. The results didn’t support this theory, as there was no statistical correlation between the genotypes and the weight loss success on the matching diet. Therefore, using these 3 polymorphisms, it is not possible to determine who will respond to a LC or LF approach. Maybe in the near future, with more genetic markers, this will be possible.
  • The link between insulin resistance (evaluated by the INS-30 in this case) was also studied. In theory, an insulin resistant person would respond better to a low carb diet. However, this study didn’t show any association between this marker of insulin resistance and the ability to lose weight on one diet over the other.
  • There were no statistically significant differences amongst all the anthropometric variables studied (blood pressure, BMI, abdominal circumference, etc.) after 12 months, except for: LDL cholesterol (5% increase in the LC group), HDL cholesterol (5% increase in the LC group) and triglycerides (15% decrease in the LC group)

Due to its large sample size, this study is an important reference in the field of nutrition and obesity. We can conclude that a “miraculous” approach to weight loss, that works for everyone, doesn’t seem to exist. Each person should experiment and find the pattern that better suits their genetic heritage. For the majority of people, food quality is, probably, more important than macronutrient ratios, and they should avoid processed foods, with high caloric density and low nutritional value.


Gardner CD, Trepanowski JF.

“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”

JAMA, February 2018

Categorias: Metabolism, Nutrition, Obesity