For people looking to lose weight quickly, limiting carbohydrate-rich foods (like fruits, starchy vegetables and grains) and prioritising those high in protein and fat (like meat, eggs and cottage cheese) has long been a reliable strategy.
But as with many ways of eating that are based on restriction, nutrition experts say that low-carbohydrate diets can come with some downsides.
“I have never recommended a low-carb diet to a patient, and I don’t plan to,” said Dr. Nate Wood, an internal medicine and obesity physician and the director of the culinary medicine program at the Yale School of Medicine.
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He and other doctors say that if you’re concerned about how carbohydrates may affect your weight, risk for developing diabetes or health in general, it’s better to focus on the types — rather than the number — of carbohydrates you eat.
What low-carb eating can and can’t do
Low-carb diets have been around for decades. Some of the first studies exploring their role in weight loss date back to obesity studies from the early 1950s. And the carb-cutting method surged in popularity after Dr. Robert Atkins published his “Diet Revolution” book in 1972.
Since then, studies have shown that limiting carbohydrates can be an effective way to lose weight. In a 2024 review of studies, for instance, researchers compared how well low-carbohydrate, low-fat and Mediterranean styles of eating helped overweight and obese adults drop a few pounds after following them for two to 18 months.
They found that while all of the diets resulted in weight loss, people on low-carbohydrate diets lost an average of nearly 6 pounds more than those on Mediterranean diets, and about 1.5 pounds more than those on low-fat diets.
Research, including a review of studies published in 2021, also suggests the diet may help people with Type 2 diabetes manage their blood sugar levels.
And the American Diabetes Association recommends low-carbohydrate eating for people who want to lower their blood sugar, blood pressure and triglyceride levels; increase their “good” (or HDL) cholesterol; and lose weight.
That said, it’s really difficult to cut out carbohydrates for a long period of time, and it’s even more difficult to do it in a healthy way, said Dr. Dariush Mozaffarian, the director of the Food is Medicine Institute at Tufts University.
While it’s reasonable to go on a low-carbohydrate diet for, say, three to six months to lose weight quickly, he said, avoiding all carbohydrates for longer than that could lead to a less nutritious diet overall.
In a 2019 review of studies, researchers said that restricting carbohydrates could cause people to replace them with less healthy foods, such as animal products high in saturated fats.
“Traditional low-carb diets are loaded with red meat,” said Dr. Frank B. Hu, a professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health. And too much saturated fat can increase the risk of developing Type 2 diabetes and cardiovascular disease, he added.
If you cut out starchy vegetables and most fruits, legumes and whole grains while on a low-carbohydrate diet, that could also mean missing out on beneficial fiber, vitamins and other nutrients that are important for cardiovascular health.
Dr Hu’s research has found that a diet low in total carbohydrates but relatively high in whole grains, healthy sources of fat and plant-based proteins can help you lose weight and slow weight gain in the long run.
Not all carbohydrates are bad
Another critique of the low-carb diet — or the phrase “low-carb diet” in general — is that it “puts all carbs in the same bucket,” Dr Mozaffarian said.
Unprocessed or minimally processed carbohydrate-rich foods — like strawberries, sweet potatoes and brown rice — take your body longer to break down than more highly processed or “refined” carbohydrates — like table sugar, white rice and white flour, he said.
The body’s rapid conversion of refined carbohydrates into glucose causes large blood sugar spikes that, if repeated over years, could result in insulin resistance, which eventually could turn into obesity or Type 2 diabetes.
That’s why the experts we spoke with recommended limiting refined carbohydrates — such as those in sodas, sugary cereals, pastries and candy. But they encouraged eating carbohydrate- and fiber-rich fruits, vegetables, whole grains, legumes and other plant foods.
Getting enough fiber (which most people don’t) reduces the risk of developing Type 2 diabetes and other major health concerns, and it feeds the good bacteria in the gut.
Fiber also slows digestion, helping you feel fuller for longer. And plant sources of fiber come with beneficial vitamins, minerals and antioxidants that are associated with better immune function, cancer prevention and cardiovascular health.
Quality over quantity
If you want to lose weight and keep it off, Dr Wood recommended focusing on the quality of the carbohydrates you eat rather than the quantity.
When eating packaged foods, it’s best to opt for those that say “whole grain” on the label, Dr Wood said. But don’t stop there, he added.
Scan the ingredients list, and if the word “whole” appears high up, that’s a sign that the product is made mostly with whole grains.
Dr Mozaffarian added that there can be a difference in how long it takes the body to break down whole-grain products, depending on how much processing the grain has undergone. It’s preferable, he explained, to choose ones that take longer to digest because they’re less likely to spike your blood sugar.
Instant oats, for example, break down in your body more quickly, whereas steel cut oats take more time. Dr Mozaffarian said it’s helpful to think of cooking time as a corollary for how long they take to digest: the longer the better.
He also recommended choosing foods that contain little to no added sugars and that offer at least 1 gram of fiber for every 10 grams of carbohydrates. If your breakfast cereal has 40 grams of carbohydrates per serving, for example, at least four of those grams should come from fiber.
Rather than cutting out all carbohydrates, Dr Mozaffarian said, keep in the good ones: “You’ll lose weight a little bit slower, but you’ll be healthier.”
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