In the history of diet research, a lot of ink has been used to print studies that claimed to resolve the great weight-loss dilemma: Should you cut carbs, or should you cut fat?
New research, however, says the answer is neither — or both, depending on how you look at it.
Indeed, a recent study from the Stanford University School of Medicine found that people who follow a low-carbohydrate diet lose weight in about the same proportion as people who use a low-fat diet.
In other words, neither diet is superior.
“We’ve all heard stories of a friend who went on one diet — it worked great — and then another friend tried the same diet, and it didn’t work at all,” Christopher Gardner, PhD, professor of medicine at Stanford and the lead author of the study, told Stanford Medicine’s News Center.
What the study revealed
The study, which was published in the Journal of the American Medical Association (JAMA), observed 600 participants over 12 months.
The participants ranged in age from 18 to 50. Half were men and half were women. All 600 participants were overweight or obese, but they were otherwise healthy.
At the start of the study, the participants were assigned to one of two groups, low-fat or low-carb.
Both groups attended regular nutrition classes throughout the course of the study. During these sessions, health educators would counsel participants to eat healthy, wholesome foods as well as eliminate carbs or fat in a way that could be sustainable over the long term.
During the first two months, participants were instructed to eat only 20 grams of carbs or 20 grams of fat, depending on their assigned category.
After that period, they were allowed small adjustments, 5 to 15 grams, and were asked to reach a balance they felt they could maintain after the study.
After the 12 months were over, the average low-fat dieter was eating 57 grams per day, while the average low-carb dieter was eating 132 grams per day.
That’s compared to the 87 grams of fat and 247 grams of carbohydrates they ate on average before the study.
The study’s leaders did not give participants calorie goals, but reports the participants filled out indicated the average person cut their daily calorie intake by roughly 500 calories.
Instead, researchers encouraged participants to make healthy decisions, such as going to the farmers market regularly, being physically active, and cooking at home more frequently.
After a year, the individual results were wide-ranging. One participant lost 60 pounds. Another gained 15 to 20.
The participants as a whole dropped an average of 13 pounds, regardless of the diet they were assigned.
Picking the best diet for you
The researchers also enrolled study participants in two pre-study activities: genome sequencing and a baseline insulin test.
These genetic and metabolic markers were previously identified as potential factors in determining how well a person might respond to a diet that greatly reduced specific nutrients, such as fat or carbohydrates.
About 30 percent of people in the test groups had genetic markers that the researchers believed indicated they’d have more success on a low-fat diet.
About 40 percent showed a “low-carb” genetic profile.
However, the profiles and markers did not correspond with any of the weight-loss results. They also didn’t help determine any participant’s weight-loss success.
Still, Gardner plans to mine the wealth of data he and his team collected and continue to analyze possible markers that can explain a person’s weight-loss opportunities.
“I’m hoping that we can come up with signatures of sorts,” he said. “I feel like we owe it to Americans to be smarter than to just say ‘eat less.’ I still think there is an opportunity to discover some personalization to it — now we just need to work on tying the pieces together.”
When a calorie isn’t just a calorie
One important factor in this study’s results may be the quality of food the participants reported eating.
On a low-fat diet, it would be easy for participants to consume a host of low-fat and no-fat foods, such as cookies, dairy products, and processed meats, and still meet their fat number for the day.
On a low-carb diet, rib-eye steaks, hot dogs, and full-fat dairy all fit because they have virtually no carbs.
However, the study’s leaders directed participants toward healthier options, whether that was whole grains for the low-fat group or lean, grass-fed proteins for the low-carb group.
They also encouraged them to eliminate processed foods such as white flour, sugary sweets, or zero-calorie sweeteners.
“We made sure to tell everybody, regardless of which diet they were on, to go to the farmer’s market, and don’t buy processed convenience food crap. Also, we advised them to diet in a way that didn’t make them feel hungry or deprived. Otherwise it’s hard to maintain the diet in the long run,” said Gardner. “We wanted them to choose a low-fat or low-carb diet plan that they could potentially follow forever, rather than a diet that they’d drop when the study ended.”
The good news out of this study for Kristin Kirkpatrick, MS, RD, LD, a licensed, registered dietitian who is wellness manager at the Cleveland Clinic Wellness Institute, is the fact that the focus on healthy, wholesome foods seems to be more beneficial than the restriction.
“I believe that [this study] will remain one of the more landmark studies due to its message that a whole foods diet is more important perhaps than the actual type of diet,” Kirkpatrick told Healthline.
“Counting calories has been shown to work in some studies, but it’s not very sustainable, and it essentially steers the individual toward caring more about quantity than quality,” Kirkpatrick said. “This is a big part of the study since a whole foods diet is one that is high in quality, could be higher in calories, and yet was effective.”
How to pick a successful weight-loss solution
While this study debunked the idea that one diet is superior to the other, or that genetic factors might influence your ability to succeed, it did show that both diet types can be successful if you’re willing to adopt the many healthy eating choices the participants were encouraged to take.
But it also showed that improving your relationship with food and choosing healthy, whole foods may actually be a smarter route than restricting or depriving yourself of specific nutrients.
In fact, Gardner said one of the benefits many study participants reported to him and his team was that the year of guided eating and nutrition classes helped them improve their relationship with food, “and that now they were more thoughtful about how they ate.”
“For most people, even a certain plan that might be more one way or more the other usually is not sustainable,” Susan Weiner, a registered dietitian and nutritionist and certified diabetes educator for more than 25 years, told Healthline. “When we talk about sustainability for the long term, something restrictive does not work. When we overly restrict like a very low-carb or very low-fat diet, it tends to make your body dulled to cues. We stop listening to ourselves because we follow a do and don’t list. When you follow a do and don’t list for too long, you don’t listen to the cues of when you’re satisfied. You don’t feel the flavors of what you’re eating.”
For now, there’s no need to try to identify which diet is best for you based on your blood type, gut biome, or any other individual marker that is promoted as the possible key to weight-loss success.
Researchers just don’t have those answers yet.
Instead, Kirkpatrick and Weiner suggest you focus on creating a healthy, sustainable relationship with foods and making choices that help you feel healthier and better overall.
“The one thing that I know is that restrictive diets don’t work in any form in the long term for anybody,” Weiner said. “What really does work is paying attention, having a good relationship with food, and really understanding why we eat and enjoying what we eat.”