Low Fat or Low Carb Diets? Which is Best?

August 21st, 2019 | Posted in Info

Previous research has shown that a range of factors such as genetics, insulin levels and the microbiome may influence how a particular diet affects an individual’s weight. Read the blog post on Genetics and Diet for more about how different genotypes respond to different diets.

A study at Stanford University looked at the effects of cutting down on either fat or carbs on weight and other aspects of health.

The study involved over 600 participants between the ages of 18 to 50, half of which were female and half male. They were randomly allocated either a low fat or a low carb diet. They followed the diet for a year.

The participants had part of their genome sequenced so that the researchers could look for specific gene patterns associated with carbohydrate and fat metabolism. They also had a baseline insulin test.

The Rules of the Study

In the first 8 weeks of the study the group eating the low fat diet were told to eat just 20 grams of fat a day or the equivalent of a handful of nuts along with carbs and protein as usual. The low carb group were told to eat just 20 grams of carbs a day, the equivalent of 1.5 slices of whole wheat bread, alongside a diet of protein and fats. After the 8 weeks the groups were told to gradually add in small amounts of fat or carbs until they reached an amount they could maintain in the long term.

At the end of the year those on the low fat diet reported an average fat intake of 57 grams. This was down from the 87 grams at the start of the study. The low carb group had reduced their average daily carb intake from 247 grams to 132 grams per day.

The Importance of Healthy Foods

The participants were encouraged to eat healthy foods on both diets. They were asked not to buy processed foods but to go to the farmer’s market instead. They were also told not to go hungry or to eat in a way that made them feel deprived. The idea was to find a diet that they could potentially follow forever.

Weight Loss

By the end of the study the average weight loss per person was 13 pounds, although there was huge variability in how much weight people lost. However, there were no associations between the genotype pattern or the baseline insulin levels and the propensity to succeed on either diet. So it seems that low fat and low carb diets both work to the same extent but that not everyone responds equally to these 2 diets.

Other Factors

The team are now considering whether the microbiome, epigenetics or a different gene expression pattern might explain the wide variability in people’s response to the diets.

What’s the Message?

The biggest take away seems to be that it may not be the fat or carb intake that is important but the switch to healthier, whole foods rather than processed foods that makes the difference. Also, that not everyone responds in the same way to food so it’s important to tune into your own body to work out what works for you.

See blog post on 6 Foods to Avoid for some simple tips about what to avoid and what to eat.


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, 2018; 319 (7