Low Carb or Low Fat Diet—The Best Way to Keep Off Weight Loss

With David Ludwig, MD, PhD, Christopher Gardner, PhD, and Caroline Apovian, MD

Lose the weight any way you like but to avoid regaining the weight, you’ll need to know how your body responds to insulin. 

For some, consuming carbs after weight loss leads to weight regain.For individuals who are insulin resistant, eating more fats than carbs will help keep lost weight off. Photo: 123rf

Wondering About Your Diet? Carbs Versus Fats

The answer to which diet is better for weight-loss and maintenance: low fat or low carbohydrate is getting clearer. In the Framingham State Food Study, David Ludwig, MD, PhD, professor in the Department of Nutrition at Harvard T.H. Chan School of Public Health, and director of the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital, looks at the impact of decreasing carbohydrates and increasing fat on caloric expenditure and weight management.1

Rather than look at the impact of these foods, Dr. Ludwig and his research team considered the problem based on how the body metabolizes the macronutrients: carbohydrates and fat, by asking: Are all calories created equal? According to the study results,1 not always, or at least not for everyone.

“The type of calories being consumed have a clear effect on the number of calories being burned,” Dr. Ludwig told EndocrineWeb, summarizing the study findings in the journal, Science.2.  According to their findings, the key to glucose management is caloric expenditure in some individuals.  

Insulin Resistance Suggests Reducing Your Carbs

Researchers from the Framingham State Food Safety Study suggest that more fats and less carbohydrates could help people with insulin-insensitivity and type 2 diabetes maintain successful weight loss better.1 The study relies on the Carbohydrate Insulin Model (CIM) of obesity,3 which Dr. Ludwig and his team pioneered, to assess the total energy expenditure (TEE) of different food types.

The CIM demonstrates that high glycemic eating patterns— resulting from a diet high in processed carbohydrates (eg, white bread, white pasta, white rice, sugar)—directs the body to store more calories as fat, rather than using the energy to support body functions.3 This switch from burning to storing calories occurs when the two metabolic hormones, insulin and glucagon become unbalanced, causing excess insulin, increased hunger, and a slowed metabolism.3 

Changing your eating pattern to one that is lower in processed carbohydrates and higher in heart-healthy fats—think avocados, salmon, nuts, olive oil, and seeds—may correct this disrupted hormone pattern. The result is an ability to burn more calories, and enabling you to more effectively regulate your weight.

The Framingham State Food Safety Study is a randomized control trial of young adults, 18-25 years, who had a body mass index (BMI) of 25 kg/m2 or more; their total energy expenditure (TEE) was monitored to measure how well they were able to burn calories during weight maintenance following a period of weight loss.1

For the first phase of the study, participants were put on a calorie-restricted diet for ten weeks to promote weight loss. During the twenty-week test phase, researchers measured the effect of decreased carbohydrates and increased fat intake on metabolic function and weight maintenance.Researchers adjusted caloric intake as needed to maintain weight loss.  Participants were randomly assigned to one of three diet groups:

  • High carbohydrate (60% carbohydrate), low fat
  • Moderate carbohydrate (40 % carbohydrate), moderate fat
  • Low carbohydrate (20% carbohydrate), high fat

Individual insulin levels were tested before weight loss to determine the relationship between insulin secretion and diet, as predicted by the carbohydrate-insulin model.

Assessing How Well the Body Deals with Types of Calories

The results of this food study showed a linear trend of an additional 52 calories burned for every 10% decrease in carbohydrate intake.1 Individuals who have the highest insulin secretion levels prior to efforts at weight loss achieve the greatest calorie expenditure, burning an average of 308 calories more daily when consuming a low carbohydrate/high-fat diet.1

However, among individuals who had normal insulin function at the outset, there was no difference in how the way their body metabolized calories from their carbohydrate intake.

These findings suggest that a carbohydrate-restricted diet is beneficial specifically for people who have type 2 diabetes and are known to be insulin insensitive.1 This makes sense if we think of insulin resistance and type 2 diabetes as a form of carbohydrate intolerance,1,3  as Dr. Ludwig believes we should. And there is support for this recommendation based on the hormone changes observed during the weight maintenance phase of the Framingham study.1

In fact, study participants in the moderate and low carbohydrate diet groups show decreases in the hormones—ghrelin and leptin—that regulate hunger. You can think of ghrelin as the short-term hunger regulator and leptin as the hormone in charge of satiety in the long-term. Leptin insensitivity is commonly seen in people with obesity and those who have metabolic syndrome.

Participants in the Framingham State Food Study had lower leptin levels in conjunction with decreased hunger and increased energy expenditure, suggesting that a lower carbohydrate, higher fat diet could help improve their glucose responsiveness.1

“The people who show the biggest declines in leptin are the most successful weight loss maintainers,” Dr. Ludwig tells EndocrineWeb.

Food Choices Affect Metabolic Function Differently After Weight Loss

It is important to know what this study does and does not tell us. To lose weight, all participants followed a calorie restrictive diet consisting of 45% carbohydrates, 30% fat and 25% protein and only participants who achieved a weight loss of 12% within that ten-week period were included in the second (testing) phase.1

 “This was not a weight loss study but rather a study specifically aimed at evaluating the effect of macronutrient partitioning on metabolic function and weight maintenance,” says Christopher Gardner, PhD, professor of medicine at Stanford School of Medicine, and director of nutrition studies at the Stanford Prevention Research Center, in Stanford , California.

Findings of Dr. Gardner’s DIETFITS study,4 in which individuals were evaluated for the amount of weight lost over 12 months, offer evidence that there is no significant difference in the number of pounds lost by participants eating a high carbohydrate versus low carbohydrate diet.

Maybe a better way to understand the impact of specific food types on weight is that “a high fat/ low carbohydrate diet is an effective treatment for people with insulin resistance than a dietary prescription for people with a normal glucose metabolism, who are trying to manage their weight,” says Caroline Apovian, MD, FACP, FACN, professor of medicine and pediatrics, at Boston University School of Medicine, in Massachusetts. But, don’t go running for that stick of butter, just yet.

Food Quality Matters: Everyone Benefits from Less Processed Foods

The type of food matters, too. “If you are eating a high saturated fat diet and you replace saturated fats with simple carbohydrates, you’re doing yourself a disservice,” says Dr. Apovian.  “But if you replace the saturated fats with mono- and polyunsaturated fats, you are following a Mediterranean-style diet and there is a lot of research to show that this is a very healthy diet,”Dr. Apovian tells EndocrineWeb. And, the moderate carbohydrate diet is essentially a Mediterranean approach to eating, Dr. Ludwig agrees.

Just as the type of fat matters, so does the type of carbohydrate. One of the biggest contributors to the obesity epidemic is processed carbohydrates.  All three researchers agree that we should stay away from processed carbohydrates, such as white flour based bread, pasta, cereal, and any foods with added sugars.  These foods are stripped of their natural fiber and other beneficial nutrients that can make carbohydrates both healthy and satiating.

What does Dr. Ludwig’s low carbohydrate diet look like?  “Limitless amounts of non-starchy vegetables, a serving or two of fruit, (eg, berries rather than bananas), an optional serving of beans, and maybe a serving of minimally processed grain or potato,” he says. 

So, are carbohydrates really the villain we’ve been warned about? Not necessarily.

For people who are insulin resistant, steering clear of low fiber, starchy, highly processed foods and increasing their intake of healthy fats instead, will improve their chances of avoiding weight regain, which is the long-term goal for improved health.

 “I don’t think we’re prepared to make recommendations yet.  This is just one study,” Dr. Ludwig tells EndocrineWeb. While Dr. Ludwig and his research team are gearing up for future studies, Dr. Kevin Hall, PhD who challenges the Carbohydrate Insulin Model for obesity is also contesting The Framingham Study’s data. 

According to Dr. Hall, the problem is the timing of baseline total energy expenditure (TEE) measurements. The Framingham Study measured TEE following the initial weight loss phase, rather than pre-weight loss.3 Why does this matter?  Dr. Hall says, “it changes the final results of the study.”  When Dr. Hall and his team reanalyzed the data using pre-weight loss TEE as a baseline, they found that “the significant increases in TEE with the low carbohydrate diet…disappeared. Dr. Hall also found that the influence of pre-weight loss insulin secretion disappeared when reanalyzing the data based on pre-weight loss total energy expenditure.6

Does this negate the findings reported by Dr. Ludwig? No.

 “The purpose of this study was to look at weight maintenance, not weight loss; to study weight loss maintenance, you want to look at people after they’ve lost weight but before you randomize them into diet groups,” Dr. Ludwig says.  As such, Dr. Ludwig chose post-weight loss TEE as a baseline before reviewing study results and explains, “This is the largest, longest, and most complex study ever to disclose the full database immediately upon publication. We want people to analyze the data and come to their own conclusions.” 

Do You Need to Avoid Carbohydrates?

 “In my personal opinion, there is likely a major difference between people’s individual biology.  People who are insulin resistant, high insulin secretors, and especially people with diabetes, will benefit the most by restricting their carbohydrates,” Dr. Ludwig tells EndocrineWeb

Who will benefit?  The easiest way to determine which individuals are high insulin secretors is by an indirect measurement obtained by evaluating body composition; people who are more apple-shaped, with fat settling around their middle, are more likely to be high-insulin secretors, says Dr. Ludwig. 

In addition, clinical tests include an oral glucose tolerance test to assess insulin response and a fasting blood glucose test to assess insulin resistance. If you think you may be glucose intolerant, discuss the need for these testing options with your doctor.

Dr. Apovian also emphasizes, “for everybody, if you focus on the quality of your macronutrients, you’ll inherently have more metabolic flexibility. Focus on minimally processed, whole foods prepared simply and the ratio of carbohydrates to fats won’t matter as much for most people.”

 In the end, food quality matters—but to some more than others. Eating whole foods, and steering clear of processed, prepared foods, is a constant theme when seeking to improve your weight and overall health, the experts agree. It is worth noting that in Dr. Gardner’s DIETFITS study,4 participants were directed away from highly processed carbohydrates, and encouraged to choose vegetables and slow-release carbohydrates (eg, minimally processed, whole grains) that have a low glycemic index.

The lastest findings clarify that for insulin resisters, steering clear of low fiber, starchy, highly processed foods will give them a greater chance at keeping lost weight off.1

Do We Have the Answer to What’s the Best Diet?

Which types of foods are responsible for increasing your girth and what diet should you follow to achieve a healthier weight? What we know now is that it may depend on how your body responds to carbs, among other things. Therefore, the solution does not lie with one single food group, but in the best overall dietary pattern that works for you personally.

That said—there IS a lifestyle treatment for type 2 diabetes, heart disease, and obesity—the answer depends on how you react to different foods and diets. When you manage to lose weight quickly only to regain the lost weight, look at what you’ve been eating, and consider the findings presented by Dr. Ludwig’s research.

One thing that all of these nutrition specialists can agree on is this: stay away from processed foods and simple sugars, don’t be afraid of fat but do choose heart-healthy fats. Eat whole foods, just not too much.7

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