Low Carb or Low Fat? It Doesn’t Make a Difference.

Ten years ago, a study was published comparing the results of four popular diets – the Atkins (low carb), Zone (low carb), Ornish (vegan/low fat), and LEARN (high carb/low fat) – among 311 women. It found a huge difference between weight lost and gained. For example, some women lost 55 pounds, while others gained 20 pounds. How could this be?

Christopher Gardner, the nutrition scientist behind the study, decided to examine this question further, hypothesizing that the issue is not with figuring out which diet is best, but determining which diet is best for each person. It’s not a stretch, when you consider how unique one’s genetic makeup, microflora, hormone responses, and lifestyle is. From the abstract:

“Rather than seeking to determine if one dietary approach was better than the other for the general population, this study sought to examine whether greater overall weight loss success could be achieved by matching different people to different diets.”

The results from Gardner’s DIETFITS study came out several months ago and have been analyzed by registered dietitian/nutritionist Carrie Dennett for the Washington Post. She praises the study for being “real world” and “sustainable” – something that participants could realistically continue doing for the rest of their lives. 

Dennett writes:

Because there’s no standard definition of “low-fat” or “low-carb,” Gardner asked the 609 participants to aim for 20 grams of carbs or fat, depending on their diet assignment. After a few weeks, they could adjust upward if needed. [He told them:]

“Please help define for the American public what is low-carb and low-fat, not just lower. What’s the lowest you can tolerate so you can look us in the eye and say, at the end of this period, ‘Yeah, I think that this place where I ended up is something I could do for the rest of my life’. ”

The low-fat group ate whole grains, legumes, low-fat organic milk, and lean meats. The low-carb group ate nut butters, coconut and olive oils, avocado, hard cheeses, eggs, and grass-fed meats. All were told to eat vegetables all day long, while minimizing refined flour and sugar.

Fascinatingly, at the end, there was no difference between the two diet types.

“The average weight loss for each group only differed by about two pounds, and each group had individuals who lost 65 pounds and others who gained 20 pounds. Neither group had an advantage when it came to metabolism slowing or fat loss vs. loss of lean muscle. The hypothesis that people who had insulin resistance (cells that resist insulin’s cue to take up glucose from the bloodstream) would do best on the low-carb diet, while those who did not would do better on a low-fat diet? That turned out not to be universally true. There was no pattern based on genetic makeup, either. Analysis based on participants’ gut microbiotas is pending.”

So, really, this suggests that neither low-carb nor low-fat is a magical formula. Either can work, in theory, depending on what you fill that dietary void with. (This is where many people go wrong, turning to overly processed or refined foods to feel satiated, rather than seeking out healthier alternatives.)

Gardner thinks that much of the study’s lasting success comes from prioritizing satiation, not cutting calories, and teaching participants how to satisfy their hunger in a healthy, wholesome way. Also, he believes that people’s attitudes toward food shifted. They cooked more food from scratch and purchased fresh ingredients – simple steps that can be real game-changers. There was also a focus on attaining satiation, not cutting calories, and knowing how to satisfy one’s hunger in a healthy way.

Michael Pollan’s advice is as relevant as ever: “Eat food, not too much, mostly plants.” And, as one commenter wisely added, “A variety of plants, mostly unprocessed, and mostly food you make yourself.”