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Low-carb vs. Low-fat: Which is better?

By Amy Richter, MS, RD, LD

It’s the age-old debate: Is low-carb or low-fat better for weight loss? Advocates on both sides have been passionately defending their opinions for years.

A new study suggests that the two may be equally beneficial for weight loss. The DIETFITS study aimed to determine the effect of a healthy low-fat diet vs. a healthy low-carbohydrate diet on weight. These researchers also wanted to know whether a person’s genetics or insulin sensitivity might determine which diet is more beneficial. They recruited over 600 overweight and obese participants who were randomly selected to follow either a low-fat or low-carb diet (equal in calories and protein) for 12 months.

The low-fat group was instructed to limit fat intake to 20 grams per day, while the low-carb group was instructed to limit carbohydrates to 20 grams per day. After two months, both groups were allowed to increase the amount of either fat or carbohydrates in their diets until they reached an amount that felt sustainable. In the end, the low-fat group was consuming an average of 42 grams of fat per day, and the low-carb group was consuming an average of 96 grams of carbs per day.

After 12 months, 481 participants remained, and there were no significant differences in weight loss between the low-fat and low-carb groups. The low-fat group lost an average of 11.7 pounds, while the low-carb group lost an average of 13.2 pounds. The individuals’ genetics and insulin sensitivity made no significant difference in weight loss.

Studies in the past have shown more weight loss with low-carb diets, but many of these studies have had small sample sizes and short durations (less than a year). The DIETFITS study is unique from previous studies because there were a large number of participants, and the duration was longer than most. Also, this study emphasized whole foods and regular meetings with a dietitian, while many others have not.

It’s important to note that both diets emphasized the following:

1. Whole foods & home-cooked meals
2. More vegetables
3. Less added sugar
4. Less refined grains

A low-fat diet comprised of white bread, sugary cereals, and few vegetables is not going to have the same health benefits that were seen in this study. On the flip side, a low-carb diet containing lots of bacon, sausage, and cheese isn’t going to be as healthy either. Also, keep in mind that the low-fat diet group consumed an average of 48% of the calories from carbohydrates, which still isn’t particularly high! The standard recommendation provided by most health organizations is that 45-65% of calories should come from carbohydrates. So, the low-fat diet in this study was still a lower-carb diet.

What’s the take-away? No matter what type of diet you follow, you should be choosing whole foods and vegetables while limiting added sugar and processed grains.

Sounds simple enough, right? But, we all know it’s not so easy to put those recommendations into practice. And some people may need more personalized diet advice. That’s why it can be helpful to see a dietitian who can help you set reasonable goals and provide accountability. If you’re ready to eat healthier and feel your best, come see me or one of the other dietitians at Achieving Your Best!

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