What We Can Really Learn From That Low-Fat vs. Low-Carb Diet Study

09/05/2014 11:31 am ET | Updated Sep 05, 2014
Kevin Twomey via Getty Images

A new study comparing low-carbohydrate diets to low-fat diets is making waves with the finding that cutting down on carbs not only results in more dramatic weight loss, but is also more successful at reducing the risk of cardiovascular heart disease than a traditional low-fat diet.

The findings, first reported by The New York Times, add to a growing debate about the role of fat in our health. A recent TIME magazine cover story declared our decades-long attempts to avoid fat in favor of carbs misguided.

While federal government guidelines have focused on low-fat eating, based on multinational studies that found a connection between traditional low-fat diets and favorable cardiac death rates, more recent clinical data paint a more complicated picture. This latest study strengthens the notion that high-protein, high-fat diets like Atkins or Paleo can be better for one’s overall health than what the government currently recommends for healthy adults: 45 to 65 percent of calories from carbohydrates, 20 to 35 percent from fat and only 10 to 35 percent from protein.

Tulane University nutrition professor Lydia Bazzano, M.D., Ph.D. and her team of researchers divided 148 racially diverse, obese men and women into two different groups: a low-carbohydrate group that was encouraged to consume only 40 grams of carbs a day (the same amount in two slices of white bread, and the same amount recommended in the maintenance phase of Atkins), and a low-fat group, which was encouraged to consume less than 30 percent of their calories from fat and 55 percent from carbohydrates (based on the National Education Cholesterol Program guidelines). For ethical reasons, Bazzano chose not to include a control group in her experiment.

Bazzano found that the low-carb group lost, on average, almost eight pounds more than the low-fat group by the end of the year. The low-carb group also gained an average of 1.7 percent more lean mass and lost 1.5 percent more fat mass than the low-fat group, despite everyone’s physical activity levels remaining steady throughout the study. Finally, the low-carb group significantly decreased their estimated 10-year risk for coronary heart disease, while the low-fat group didn't.

The low-carb group made these gains despite the fact that they, on average, never reported meeting their 40 grams/day carb goals during the three “check-ins” throughout the year. They ate more than double and at times even triple the amount of carbs they were directed to eat every day, but those elevated levels were still about half as many carbs as the low-fat group was eating. The low-carb group also upped their protein over the course of the year, going from 18 percent of calories from protein to 25 percent by the end of the year.

The low-fat group, on the other hand, seemed to replace their fat not with protein, but with more carbohydrates, above and beyond the 55 percent from calories that Bazzano's team recommended.

Walter Willett, M.D., Dr.P.H., chair of the department of nutrition at the Harvard School of Public Health, who wasn’t involved in the new research, praised the study for the way it was conducted. For Willett, the most important feature about Bazzano’s study was the equal intensity of dietary counseling for both intervention groups -- which in and of itself has been shown to have an effect on weight. But he demurred from proclaiming one diet superior to the other, instead espousing a “whatever works” attitude.

“These are the average results, and some people [would] do well on either diet," Willett wrote in an email to HuffPost. “The key issue for each person is finding a way of eating that is healthy and can be maintained for the long term.”

Brad Johnston, Ph.D., a professor of clinical epidemiology at McMaster University in Ontario, Canada, agreed with Willett, noting that comparable results could be achieved with other diets and that the desirable results from Bazzano's low-carb diet over the course of the year could simply be due to diet adherence. (The low-carb dieters in the study lost an average of more than 14 pounds, experienced a 7-inch decrease in waist circumference, and also had lower blood pressure, cholesterol and triglyceride levels.)

Johnston recently authored a meta-analysis of other randomized, controlled trials that compared different classes of diets and found that there was no significant difference in weight loss results between several low-carb, low-fat and moderate macronutrient regimens. His meta-analysis was one of the first to synthesize randomized, controlled trials that tested different branded diets, and the experiments had both at least six-month and 12-month follow ups.

“The take-home message is that people should choose a diet they can best adhere to, given that the differences [in results] between them are minimal,” Johnston told The Huffington Post. Still, in congruence with the Tulane study, Johnston found that the low-carb and low-fat diets stood out as the most effective diets after six months and 12 months.

As for the Tulane research itself, Johnston said that while the methods used in the study were of high quality, showing that perhaps low-carb diets are good for some cardiovascular risk factors, people should still not make a dramatic lifestyle change based on these findings.

But for anyone who wants to approach their doctor about a low-carb diet based on the results of the Tulane research, it's important to consider that the diet itself was just one component of the study’s intervention for both groups.

Bazzano said that she did indeed make adherence a key goal for both the low-carb and low-fat groups, which perhaps explains why her study shows lower-than-average study drop-out rates (82 percent of participants in the low-fat group and 79 percent of the low-carb group completed the year-long study).

Throughout the course of the year-long intervention, both groups had access to private appointments with nutritionists, community support and "accountability measures." In a phone interview with HuffPost, Bazzano described one such measure:

We tried to develop very close relationships with participants. We also gave them a behavioral commitment contract. They had to sign that they were really committed to doing the study, and that they understood this was a long-term lifestyle change study -- in addition to their consent, of course. Sometimes, if a participant felt like dropping out, we’d call on the phone, send a card and include the signed commitment form that said they were willing to do this for a whole year.

Bazzano’s behavioral modification curriculum also included advice on how to plan meals, order healthy food from restaurants, avoid overeating triggers and control portion sizes. Participants learned about mindful eating, a technique that emphasizes the ability to feel when you’re full, slow down the eating process and pay attention to the sensation of eating.

And both groups were also encouraged to eat monounsaturated fats like olive oil and canola oil while avoiding trans fat, which is found in processed food.

“We wanted them to have more of an understanding of the sorts of things that would help them lose weight,” regardless of what the proportions of their diet were, Bazzano said. This comprehensive approach may partly explain the fact that both groups significantly lowered their average daily calorie consumption over the course of 12 months, despite the fact that they were never given a calorie goal. For the low-carb group, the average calorie consumption per day went from 1,998 calories to 1,448 calories, while the low-fat group went from 2,034 calories to 1,527 calories.

In other words, Bazzano planted the seeds for lifestyle change, challenging participants to completely rethink their relationship to food the way that all behavior-modification programs around weight ought to do. However, she disagreed that her study simply showcased the power of adherence to a diet.

“If you are an obese person with high cholesterol, I think you’d be highly unlikely to hear from your health practitioner that you should go on a low-carbohydrate diet,” said Bazzano. “The public perception is that a diet high in fat could not possibly be healthy, but in fact it is healthy and is doing an even better job of lowering cardiovascular risk, according to my study.” Indeed, the low-carb dieters in her study went from consuming an average of 32.5 percent of calories from fat at the beginning of the study to 40.7 percent by the end of the year, most of it healthy monounsaturated fat.

Because the majority of dieters gain back all the weight they lost and more after four to five years, a long-term study on which diet is best is the most valuable perspective of all. Those studies are few and far between, and the ones that do exist reveal a depressing truth: Not only are you likely to gain lost weight back, but going on a diet and losing weight is in fact a very reliable predictor that you will gain weight in the future.

Bazzano hopes to take this on one day and follow a smaller group of dieters for a longer period of time to see if there are any ultimate differences between the two.

Also on HuffPost:

5 Signs You Should Be Eating More Carbs

CONVERSATIONS