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Low-carb diets have long been touted as being beneficial for weight loss, diabetes and other medical conditions. This focus on carbs is largely due to how the body uses them: The body uses carbs for energy, but when carbs are restricted, the body turns to its fat stores for energy. This is what typically leads to weight loss.
Additionally, a diet high in simple carbs (like pastries, white breads, cookies and some prepackaged foods) is associated with an increased risk of chronic disease, like diabetes and obesity.
If you’re considering a low-carb diet, read on to learn more about the efficacy and safety of this type of eating plan.
In addition to their role in providing energy, carbs also help regulate blood sugar, insulin metabolism and support cholesterol and triglyceride metabolism. When there is an overabundance of carbohydrates in the diet, these bodily functions can be thrown out of whack.
Dietary carbs can be divided into the following categories:
Dietary guidelines recommend individuals fill 45-65% of their diet with carbohydrates, with a focus on having an optimal fiber intake and limiting simple carbs[1].
Low-carb diets typically provide around 20 to 130 grams of carbs per day and anywhere from less than 10% to 44% of calories from carbs[2]. Some of the more popular low-carb diets include the following:
Keto diets typically include 20 to 50 grams of carbs per day. “[This] diet gained attention in the early 20th century when physicians discovered the beneficial effects of carb restriction on the symptoms of epilepsy in children, therefore, these diets were used for the treatment of epilepsy,” says Alma Simmons, a registered dietitian nutritionist and maternal fetal medicine dietitian and diabetes educator at Ohio Health Hospital. “However, when people started realizing that low- carb diets could also help with weight loss, the popularity increased drastically,” she adds.
The goal of the keto diet is to induce ketosis. Typically, the body prefers carbs as its main fuel source, but when there aren’t enough carbs available, the body is forced to burn stored fat for energy. Ketosis is the name of this fat-burning process.
It’s important to note that a keto diet designed for an individual living with epilepsy is quite different from one designed for someone who does not have the condition. Most notably, individuals with epilepsy are routinely advised to go on a more restrictive, very high fat diet so their body goes into ketosis quickly.
Established in 1972 alongside Dr. Robert Atkins’ book Dr. Atkins’ Diet Revolution, this diet is based on the idea that a low carb intake—as opposed to the conventional low calorie diet—is superior for weight loss. Today, there are variations of the Atkins diet, ranging from 20 to 100 grams of carbs per day. Typically, the Atkins diet is less restrictive when it comes to fruits and vegetables, which may make it a good choice for increased consumption of vitamins and minerals.
Proponents of the paleo diet claim that the foods eaten by hunter-gatherer groups from the Paleolithic era are best for human health. The diet contains about 25% carbs and excludes all grains, legumes, dairy, sugar and processed foods.
Different people may respond differently to low carb diets; just because a certain low carb diet works for one person really well (i.e quicker weight loss), doesn’t mean it will work the same way for another person—a distinction often due to genetics. Additionally, individuals living with extra weight and obesity may find that it takes them longer to reach ketosis than individuals who are not living with those conditions.
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“When you restrict carbohydrates from your diet, the macronutrient intake of fat and protein generally increases to compensate,” says Simmons. The following foods are typically eaten on low-carb diets:
Low-carb diets generally advise limiting or eliminating the following:
Depending on the low-carb diet, starchy vegetables, dairy and fruits may also be limited or avoided.
While many people tend to turn to low-carb diets for weight loss, the research around this effect is not completely cut and dry. A 2022 Cochrane Database systematic review looked at 61 randomized controlled trials with nearly 7,000 participants placed on either a low-carb diet (less than 45% of total energy) or balanced-carb (45% to 65% of total energy) diet[3].
Interestingly, findings showed little to no difference in weight loss in both participants living with type 2 diabetes and participants without type 2 diabetes, especially over the long term (one to two years).
While weight loss may be achievable on a low-carb diet, research has shown that the initial weight loss is at least partly due to loss of water weight. Fat loss does tend to happen with diet adherence, but after adherence wanes, the effect is similar to other diets after one year.
And adherence is known to wane. According to a 2021 study in Nutrients, long-term adherence to a low carb diet (specifically keto) was difficult for most participants[4].
The true answer to whether low-carb dieting is effective for weight loss is “complicated,” explains David Prologo, M.D., a double board-certified interventional radiologist and obesity medicine specialist at Emory University School of Medicine. He explains that “a low-carb diet may be a helpful component of a successful weight loss program, but only if many other things are attended to as well, such as fluid choices, recovery, hunger management, exercise and more.”
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In the short term (approximately six months), a low-carb diet can be helpful for individuals living with type 2 diabetes, increasing remission rates of the condition, reducing medication use, increasing weight loss and improving triglyceride levels, according to a 2020 review and meta analysis in BMJ[5]. However, that same review found that by 12 months, most of the benefits of a low-carb diet diminished, and even seemed to worsen LDL (bad) cholesterol.
A low-carb diet is indeed an option in the medical nutrition therapy for diabetes, per the American Diabetes Association (ADA) guidelines. However, the ADA emphasizes that low-carb diets are certainly not the only dietary treatment available, and macronutrient (carb, fat and protein) recommendations should be individualized and based on eating patterns, preferences and goals.
Echoing the BMJ study, many nutrition experts remain cautious or even wary of low-carb diets.
“[Low-carb dieting] reduces food to its macronutrients (fat, protein, carb) and ignores the thousands of phytonutrients in carb-rich plant foods as well as the vitamins, minerals and the wide variety of fibers that are found only in carb-containing foods,” explains Jill Weisenberger, M.S., a registered dietitian, certified diabetes care and education specialist and creator of the digital Prediabetes Meal Planning Crash Course. She adds that these nutrient-dense plant-based foods “are so important in the prevention and treatment of diabetes and other chronic diseases.”
When it comes to the ability of a low-carb diet to lower inflammation to statistically relevant levels, current research remains mixed.
While research shows that weight loss can improve outcomes in individuals living with extra weight and obesity who also have rheumatoid arthritis, when it comes to the potential anti-inflammatory effects of low-carb diets in this setting, a 2021 review concluded that the evidence thus far is limited and further studies are needed to draw conclusions[6].
Chronic inflammation is a key factor in the development of Alzheimer’s disease. In a 2018 review, researchers observed potential neuroprotective effects in people living with cognitive impairment or Alzheimer’s who were placed on a keto diet. They explained that ketone bodies appear to decrease oxidative stress and perform anti-inflammatory activity. Still, study authors stressed the need for more clinical trials to validate these preliminary findings[7].
Like any restrictive diet, low-carb diets can come with certain adverse effects, most notably when undertaken over the long term. Some of these adverse effects include:
Children, young athletes, pregnant and lactating individuals and people struggling with or have a history of eating disorders would not be good candidates for low-carb diets, says Simmons.
All in all, the efficacy of low-carb diets remains in question, especially in broader contexts. However, there are certain situations—such as when an individual is looking to lose weight or ease symptoms of type 2 diabetes in a short period of time without restricting calories—in which it may be beneficial. If you or someone you know is interested in following a low- carb diet, it’s always recommended to talk with your doctor or a nutritionist first to see if the pros and cons of this particular eating plan are best for your personal health history.
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Johna Burdeos is a family mom, registered dietitian and freelance writer. Having provided nutrition care to many patients with acute and chronic medical conditions over the years, Johna is passionate about engaging the public in prevention and nutrition with simple steps toward change. A Filipino-American, California-bred and Texas resident, Johna enjoys walking, working out along to YouTube videos with her kids, and cooking and sharing hassle-free recipes with minimal ingredients. Johna’s nutrition philosophy is MVP for moderation, variety and patterns. She not only believes in the nutrition of food but also in the joy it can bring and the way it connects and builds bridges across the table.
Dr. Taylor C. Wallace is principal and CEO of the Think Healthy Group—a food science and nutrition research firm—as well as a professor in the department of nutrition and food studies at George Mason University. His academic research interests are in the area of nutritional interventions to promote health and prevent the onset of chronic disease. He is the author of the online blog and educational platform www.drtaylorwallace.com and is regularly seen on NBC4 Washington and the Dr. Oz Show.
