Best Diet for Weight Loss, Your Choice: Low Carb vs Low Fat

With Christopher Gardner, PhD, and Carolyn Apovian, MD

You're determined to lose weight this time and find yourself debating whether to go low-fat or low-carb? 

Pick the one you are most likely to stick with, says Christopher Gardner, PhD, professor of medicine at the Stanford Prevention Research Center at the Stanford University School of Medicine in California who compared both diet regimens for the best weight loss.The researchers concluded that you can expect to lose the same amount of weight, on average, on either one.  

"Whichever diet you prefer could work," Dr. Gardner, PhD, indicating this was one key finding from the study1 published in the Journal of the American Medical Association.

Besides comparing low fat and low carb eating plans for weight loss, Dr. Gardner and his colleagues also looked at whether levels of insulin production or genetic factors affected individual weight loss and made one diet better than another among those trying to lose weight, as some experts have suggested.1 They found that neither insulin levels nor genetics made any difference in a person’s ability to lose weight on either of the diet approaches.

Comparing low fat to low carb diet, both achieve equal weight loss.Choose a low-fat or low-carb diet to lose weight. What really matters is your relationship to food going forward.

Comparing Weight Loss Following Less Carbs and Less Fat

In the 12-month study, which began in 2013, the Stanford researchers assigned 609 overweight men and women to the low carb group or the low-fat group.1 In all, 241 participants on the low-fat diet and 238 individuals on the low-carb diet finished the study. Those in the low-fat group were told to cut back on fatty meats, whole-fat dairy products, and nuts, for instance; and those in the low carb group were instructed to cut down on rice, cereals, bread and pasta (eg, grain-based foods). There was no calorie limit, just a focus on the types of foods they had to eat less of.

Participants went to classes to learn more about each diet type. No restrictions were made on total calories. Those on each diet were told to limit either fats or carbohydrates to 20 grams a day the first 8 weeks, then to slowly phase in the lowest level of intake on either fats or carbs they believed they could maintain. They did this with the help of the experts.

A typical breakfast for those in the low-fat group was steel-cut oatmeal with skim milk and berries and black coffee, Dr. Gardner says. For those on the low-carb plan, a typical breakfast was three or four scrambled eggs and black coffee with cream.

"Over one year, the low-fat group lost 12 pounds on average," he tells EndocrineWeb, and "group following the low carb diet lost about 13 pounds."

Is Diet Composition Influenced by Differences in Insulin or Genetics? 

Findings from past research have pointed to changes in insulin levels to explain different success rates in people following certain types of diets.2-6  For instance, it was proposed that people with greater insulin resistance may do better following a diet low in most carbohydrates because of the decreased demand on insulin.  However, in this study,1 Dr. Gardner said, “there was no indication that a low carb diet was any better for those with insulin resistance than a low-fat diet.”

As for genetics, certain genotype patterns, specifically related to three genes that help regulate fat and carbohydrate metabolism, are believed to predict who will do well on different diets.7 However, in this study, the researchers calculated each person's genotype patterns and found that the type of diet did not make any difference in the amount of weight the individuals lost.1

Looking More Closely at the Study Findings

The study was well done, but has some important limitations, says Caroline Apovian, MD, FACP, FACN, professor of medicine and pediatrics, Boston University School of Medicine, who reviewed the study for EndocrineWeb.   

The individuals enrolled in this study may have ''cheated,'' Dr. Apovian suggests, by not adhered completely to the low-fat or low-carb plan. This is very common and even expected.

The information about insulin secretion and genetic patterns having no effect is new and useful information, Dr. Apovian says; however, ''the story is not over yet'' on those points. Another large study is underway, with results expected soon, that may shed additional light on those factors.3

Meanwhile, Dr. Apovian tells her patients, most of whom have insulin resistance, to eat a diet lower in carbs, particularly grains. "There are short-term studies that show diets that contain more protein and [healthy] fats are satiating," she says, so people are more likely to stay with them.

The Secret Isn't the Diet But the Ability to Make a Long-Term Commitment

Gardner says the other important point from his study is the range of weight loss on both diets.1 Some people lost 40 or more pounds, he says, while others gained 10 or 20. What might have worked differently for the more successful losers?

"People who did the best credit us with helping them change their relationship with food," he says, regardless of the type of diet they were on.1 By selecting the type of diet they could stick to, their weight loss, he says, has less to do with whether the diet is low carb or low fat. Rather, it has much more to do with behavior change: "mindfulness, putting the fork down, not eating in front of the screen, going to the farmer's market, cooking meals."

Of course, losing some weight, any weight is important to reduce health risks, but it will serve individuals best if they can maintain the lost weight so committing to changes in their relationship to food matters most, the experts agree.

Dr. Gardner reported no relevant disclosures. Dr. Apovian has participated on advisory boards for Amylin, Merck, Johnson and Johnson, Arena, Nutrisystem, Zafgen, Sanofi-Aventis, Orexigen, EnteroMedics, Scientific Intake and Novo Nordisk and she is on the Takeda Speakers' Bureau for the medication Contrave and has an ownership interest in Science Smart LLC.


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