The low carb vs low fat diet for weight loss has been debated at length. The ultimate question is does it make a difference in weight loss when choosing a low carb vs low fat diet. There has been a great deal of research on this topic. Recently an article on the DIETFITS Randomized Clinical Trial was published in the Journal of the American Medical Association helping us answer this question.

Randomized clinical trials (RCTs) are one of the best methods of research. RCTs provide scientifically tested answers to tough questions. This study was particularly good because it studied over 600 overweight people. It is always nice to study a large number of people as smaller studies may either prevent you from seeing a significant (mathematical statistical difference) or make you think there is a difference when there is or isn’t one just by chance alone.

So in this study over 600 overweight people were observed while following either a low fat or low carb diet. The people in the study were monitored for an entire year. The participants were counseled on healthy food choices depending on the diet they were randomized to.

Low Fat Diet

The people on the low fat diet had a macro breakdown of 48% cards, 29% fat, and 21% protein.

Low Carb Diet

The people on the low carb diet had a macro breakdown of 30% carbs, 45% fat, and 23% protein.

The weight change was a loss of 5.3kg (11.6lbs) for the people on the low fat diet and loss of 6.0kg (13.2lbs) for those on the low carb diet. This difference was not statistically significant, meaning the difference in weight loss between the two groups could have happened by chance alone. However, over 10lbs of weight loss is great!

There was no strict caloric limit set, just essentially instruction on choosing healthy foods and limiting calories from certain categories based on the diet they were randomized to. Each person at the start of the study was limited to either 20g/carbs or 20g/fats. People then increased those in small increments each week until they felt they were at a comfortable diet they could sustain. It was determined that both groups were in around a 500-600 calorie deficit.

Both groups received basic information such as

1. Maximize vegetable intake.
2. Minimize added sugars, refined flours, and trans fats.
3. Focus on whole foods that were minimally processed.

My take away from this study is similar to most of the information that we have put out before calories are what matter. To lose weight you must be in a caloric deficit. It matters much less the exact break down of the macronutrients that you consume. This study reinforces that you can pick a diet what works best for you body/lifestyle. If you can find a diet that you can stick with consistently and maintain a caloric deficit you will likely find success in your weight loss journey.

Sources for low carb vs low fat diets:

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.