A Low-Carb Diet Isn’t the Cure for Insulin Resistance — In Fact, It Might Do More Harm Than Good

Ask anyone what causes diabetes, especially someone with the condition. Most will say it’s the sugar and the carbs — sodas, sweets, pasta, bread, and potatoes. So once people get their diagnosis, most new patients try to limit these foods. Most doctors will advise to eat them sparingly, if at all. “But the cause of diabetes is not eating sugar or carbohydrates,” says Neal Barnard, MD, author of Dr. Neal Barnard’s Program for Reversing Diabetes. “I think that one day, this conventional medical approach to prescribe a low-carb diet to people with diabetes will be considered old-fashioned, if not malpractice.”

Unlearning a Fear of Carbs

It’s true that foods high in carbohydrates can trigger a spike in blood glucose if someone has developed an inability keep sugar levels stable. So avoiding these foods can help keep glucose numbers in check. This is the barometer by which most people monitor their disease. “But if you starve yourself of carbohydrates on a low-carb or ketogenic diet, you’re just saying, ‘Well, I know my body can’t handle carbs. I know that ability is broken. So I just won’t eat any,’” says Barnard, an adjunct professor of medicine at the George Washington School of Medicine at George Washington University in Washington, D.C. “And people who do that, and who are able to maintain low blood sugar levels, will call that remission — but I think it’s nonsense to call it that.”

That’s because low-carb eating is merely a way to mask signs of the disease. Managing glucose levels in this way is not reversing the condition. The key to the cure is targeting how diabetes develops. Diabetes starts as insulin resistance and, in someone with Type 2 diabetes, this can take years to develop. “A lot of people have insulin resistance, but they may not get diabetes if the cells in their pancreas are still healthy and cranking out so much insulin that they can overcome the resistance,” explains Barnard, who has published research on reversing the condition.

When Cells Say ‘No’ to Insulin

Insulin is the hormone secreted by the pancreas when carbohydrates and protein are consumed. Carbohydrates are digested and broken down into glucose molecules. Protein is digested and broken down into amino acids. Both are absorbed into the bloodstream from the digestive system. From there, insulin takes the glucose and amino acids from the blood and delivers them to cells that can use the glucose for energy or the protein to build things that the body needs. If there are extra glucose molecules or amino acids that can’t be used or stored, they both get converted into body fat.

This tightly regulated system goes haywire when cells stop responding as well — and start resisting the insulin that’s trying to shuttle glucose in. So the pancreas whips into overdrive and produces more insulin to overcome the resistance. At some point, the pancreas fatigues. It can’t keep up with the demand, so inadequate insulin is produced to handle the onslaught of glucose coming in. Or insulin receptors on cells take in less and less of the glucose that’s circulating. Or both. So glucose builds up, hovering dangerously high and loitering in the bloodstream, where it can do damage to different parts of the body since blood travels through vessels everywhere.

Understanding the Cause

What causes cells to resist insulin? “Fat buildup inside the cells,” says Barnard. Excess dietary fat, especially saturated fat, gets stored in cells and then triggers insulin resistance. And as insulin resistance progresses, the more out of control blood glucose becomes. Therefore, current medications can become less effective, requiring increases in dosage.

Many people do not understand what insulin resistance is, and more importantly, what causes it. What is surprising to many people is that what they are eating to control their blood sugar may be simultaneously causing a progressive worsening of their insulin resistance — and a worsening of their Type 1 or Type 2 diabetes. “If you stop eating carbohydrates, what’s left is mostly protein and fat — the fat in meat, chicken, and cheese — and they are all high in saturated fat,” says Barnard. “What kills someone with diabetes? It’s not the high blood sugar — they’re most likely to die from cardiovascular disease, and by eating a high-fat diet you’ve just made that much more likely.”

Monitoring blood glucose is important. However, addressing the root of the issue is what will ultimately help you beat diabetes. “Anything you can do to target and reverse insulin resistance is the key,” says Joyce Vergili, EdD, RDN, CDN, a kidney and diabetes specialist in Kingston, New York. “There are a number of ways to do that, including exercise, decreasing saturated fat, decreasing processed sugar, and losing weight.”

Pros and Cons of Low-Carb Diets

Avoiding high-carb foods and processed foods high in sugar and low in fiber isn’t a bad thing. It can often lead to some healthful choices — like eating more vegetables. But fruit intake often suffers. “One of my biggest concerns with a low-carb diet is that often people restrict very healthy foods like fruits, and fruit is associated with a reduced risk of pretty much every chronic disease,” says registered dietitian Karen Smith, MS, RD, based in Washington, D.C. “People with diabetes who consume more fruit have a reduced risk of all the complications of diabetes.”

Of course, people lose weight eating low carb. And even small amounts of weight loss can improve diabetes, no matter how that weight is lost. But you can lose weight from a high-carb diet, too. It’s the cutting calories that causes the improvement, not always the foods.

Beware of tunnel vision from focusing only on glucose numbers. “Improved glycemic control and weight loss are considered to be soft endpoints in research,” points out Joel Fuhrman, MD. His most recent book, Eat for Life, highlights how what he calls a nutritarian diet can reverse chronic disease. “You see the hard endpoints with longer term studies: the age when someone dies, if they have a heart attack or if they die from one.”

And caution is warranted. Multiple studies have shown that the hard endpoints from low-carb diets are bad news. A study in The Lancet followed more than 15,000 adults over 25 years and found that those who ate lower-carb diets had a higher risk of death.

The Power of Plant Foods

In the Lancet study, the source of the protein and fat in their low-carb diet made a difference. When participants ate more animal fat or animal protein from beef, chicken, pork, and lamb, their risk of death increased. When they included more plant-based fats and proteins from vegetables, nuts, peanut butter, and whole grains, their risk of death decreased. “The most striking finding in the scientific literature is that more animal protein in the diet accelerates early death from all causes, including cancer, stroke, and dementia, while more plant protein enhances lifespan and reduces death from all causes,” says Dr. Fuhrman.

“There have been a lot of studies in the last five years or so showing that people on various low-carb diets like paleo or keto or using varying degrees of animal products long-term had an increased risk of early death, even when glucose was better controlled,” says Fuhrman. “You can manage glucose and body weight with these sorts of dietary gymnastics, but the healthiest way to eat long-term is a diet higher in low-glycemic, whole plant foods such as beans, greens, nuts, and seeds.”

Studies also consistently show that the nutrient density of the food you eat matters. In The Lancet study, high-carbohydrate diets that consisted of poorer quality, refined foods like white rice and white bread also showed an increased risk of death, although not as high as the low-carb diet demonstrated.

Reversing Insulin Resistance

Exercising and eating fewer calories overall and fewer processed high carbohydrate foods are all good lifestyle choices. They can all help burn fat and lose weight, improving insulin resistance. But the key to removing that stored fat from the cells in your muscles, liver, and pancreas is to eat less of it. This especially goes for saturated fat, which is predominant in animal foods like dairy and meats. Some plant foods such as coconut and palm oils have high amounts of saturated fat, too. And keep in mind that any food contains an array of different amounts and types of fatty acids. So generally all foods have some saturated fats and unsaturated fats. It’s just the proportion of each that varies in different foods.

Find the Diet That’s Right for You

While fish and chicken are often believed to be healthier than red meat, they both contain saturated fats and eating too much of either still adds up. A plant-based diet that is high in fiber will naturally be low in fat. However, it will include enough of the essential fats that your body needs to thrive. “I have found that people love eating this way, even if they might not think they will at first,” says registered dietitian Smith. “People can eat fruit again, and beans and lentils and whole grains, even potatoes — there’s such a huge variety and in so many different cuisines — Indian, Thai, Greek, Italian. I’ve found that patients are excited to feel like they have permission to eat these foods, because they’ve been told for so long not to. That is one of the biggest rewards.”

This content is not a substitute for professional medical advice or diagnosis. Always consult your physician before pursuing any treatment plan.

A version of this article appeared in our partner magazine, The Complete Guide to Reverse Diabetes, in 2022.