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Should you cut fat or carbs? Study offers new answers in the diet debate

A new study comparing cutting carbs with cutting fat finds one approach provides a slight advantage when it comes to weight loss.
/ Source: TODAY Contributor

It seems like everyone is cutting carbs to try to lose weight and barely a day passes without someone touting the benefits of a carb-free life. But a new study comparing cutting carbs with cutting fat finds slashing fat provides a slight advantage when it comes to weight loss.

“It is best if you … cut the carbs or fat?” says Kevin Hall, a metabolism researcher at the National Institute of Diabetes and Digestive and Kidney Diseases and author of the study, which appears in Cell Metabolism.

“This is a direct test of whether or not it matters.”

Read more: For your health, should you try paleo or Mediterranean diet?

To understand whether simply eliminating one macronutrient, such as fat or carbs, affected diet, Hall asked 19 overweight people to agree to stay in a secure ward, where all their food was monitored for two, two-week periods.

During the first visit, people ate fewer carbs — 800 calories worth — with no cuts to their protein and fat intake.

During the second visit, people ate less fat — 800 calories worth — with no cuts to their carb and protein intake.

The participants also exercised for an hour each day during both stays.

“The study does, in fact, show more fat loss with the low fat diet,” says Hall. “The differences we were measuring were kind of small.”

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Hall found cutting 800 calories of carbs a day meant people ended up losing fat at a rate of 53 grams per day. But cutting 800 calories of fat meant people shed fat at a rate of 89 grams per day.

This matched what he had found in computer models on metabolism and fat loss: Low-fat diets lead to more overall fat loss.

To lose a pound of body fat people must drop 454 grams of it; a loss of 89 grams “is very minimal — 3 ounces,” says Leslie Bonci, owner of Active Eating Advice.

While it might seem as if the study suggests low-fat diets work slightly better than low-carb diets, that’s not the true takeaway, experts say.

“If you cut calories, every diet works. The thing that is most important is to find a plan that works for you,” says Madelyn Fernstrom, NBC News health and nutrition editor.

“People need to worry less about the specifics of the macronutrients — is it high or low fat— as long as it is balanced.”

Read more: 'Hangry' and thirsty? 6 signs it's time to fire your diet

When selecting a diet, Fernstrom recommends people think about it as something that feels sustainable, allowing them to maintain their weight loss.

“How connected are you to this plan and can you look at this as a lifestyle and not a diet?” she says.

One drawback of the study was that the sample size was small. But Bonci says the findings reinforce what other studies found.

“It is a small study and [we might need to] take it with a teaspoon of oil,” she says. “I think it is just one more reason why it is not going to be one size fits all when it comes to people (and) weight loss.”