Keto Debate: Is Low-Carb a Game Changer or a Risky Gamble?

WebMD

02-06-2025

With one glaring exception. Recent estimates show that 13 million Americans follow a ketogenic diet – a nutrition paradigm based on extremely low carbs and high fats – and its popularity is only growing.
"This one's hardly a fad, since it's over 100 years old," said Ethan Weiss, MD, a preventive cardiologist at the University of California, San Francisco.
Stores like Costco, Kroger, and Target today advertise "keto-friendly" products to help followers stay the course, and keto snacks are getting more popular among younger consumers. The market size for keto is $13 billion today, and projected to be worth over $16 billion in 2030.
Enthusiasts swear by its health benefits: rapid weight loss, better appetite control, lower blood sugar levels, reduced insulin spikes, and decreased inflammation. "Keto diets have been shown over multiple studies to be beneficial in terms of weight loss and, at least to some degree, in helping the treatment of diabetes," said Weiss.
Yet keto diets directly challenge decades of research showing that consuming high amounts of fat over long periods harms your health, in particular heart health. Unlike more widely recommended eating patterns, such as the Mediterranean diet and DASH (Dietary Approaches to Stop Hypertension), keto is highly restrictive and hard to maintain, and lacks long-term data.
So who's right – mainstream nutrition scientists or keto aficionados? That question has received a lot of attention in recent research. And while a conclusive answer may be years away, current evidence urges caution when it comes to going all in on keto.
Ketones as Fuel
Originally developed in the 1920s as a treatment for epilepsy, the keto diet dramatically reduces how many carbs you eat. This mimics the metabolic effects of fasting, forcing the body into a state of "ketosis" – when the liver starts converting stored fat into ketone bodies (an alternative energy source when glucose, or sugar, is scarce). Doctors found that the diet could significantly make seizures less frequent and less severe, particularly in children who did not respond well to other treatments.
Typically, the U.S. Department of Agriculture recommends people eat a diet consisting of about 45%-65% carbohydrates, 10%-35% protein, and 20%-35% fat. Total calorie intake recommended for Americans is 1,600-2,400 for women and 2,000-3,000 for men.
Following a keto diet means shifting the percentages of fats, carbs, and protein to 70%-80% fat, 5%-10% carbs, and 10%-20% protein. If you eat 2,000 calories a day, that amounts to 20-50 grams of carbs (about two to three slices of bread), 75 grams of protein (10 ounces of beef, chicken, or turkey), and 165 grams of fat (11 tablespoons of peanut butter, or 10 avocados).
Eating fewer carbs reduces glucose levels, prompting your pancreas to produce less insulin. Since insulin promotes fat storage, having less of it helps keep fat from building up. Combined with ketosis, this fat-burning state can make low-carb diets work better for weight loss than low-fat ones, research suggests.
The drastic shift can lead to short-term side effects like fatigue, headaches, crankiness, and brain fog – what some refer to as the "keto flu." This can make the diet hard to follow, as do the very strict guidelines on nutrient proportions. That's part of the reason keto is so appealing to the food industry: Demand is high for products that simplify the preparation of high-fat, low-carb meals.
Still, keto backers say once the first few weeks are over, the flu-like symptoms disappear and meal prep becomes second nature.
But these challenges aside: Is keto truly a healthy choice?
Benefits and Risks of Keto: What the Research Shows
A 2023 big-picture review, published in BMC Medicine and covering 17 meta-analyses of 68 randomized trials, found that keto diets can improve triglycerides, body weight, and blood sugar levels in adults with overweight or obesity – and reduce seizures in patients with epilepsy.
A 2025 study also highlights how cutting carbs and entering ketosis can lower body mass index, waist size, and visceral fat – highlighting the power of keto for weight management.
Other research confirms that the keto diet consistently improves markers of metabolic syndrome – a collection of conditions that raise the risk of heart disease, type 2 diabetes, and stroke. It's also been shown to improve cholesterol levels, reduce inflammation, lower blood pressure, and even slow vascular aging (changes in your blood vessels as you get older).
Yet for all the benefits, research also highlights serious concerns, including nutrient deficiency, increased heart disease risk, and higher levels of LDL cholesterol (the kind that can build up in arteries and cause heart problems). The BMC Medicine review, too, found a significant increase in LDL cholesterol, underscoring the need for long-term trials to assess keto diets' impact on the health of the heart and blood vessels.
"The concern is that ketogenic diets are going to raise the level of your cholesterol, and that will be harmful for your heart in the long term, even if there are short-term benefits related to weight loss," said Sadiya Khan, MD, a professor of cardiovascular epidemiology at Northwestern University Feinberg School of Medicine.
Those happy with their waistline on keto may dismiss the negative effects. "They're trying to convince themselves that what I consider to be an alarming increase in LDL cholesterol is not dangerous," said Weiss. "That's the single biggest drawback as to the long-term safety of these diets."
Cutting way back on carbs means you likely have to sacrifice whole grains, fruits, and vegetables, leading to deficiencies in fiber, vitamins, and antioxidants that supplements can't make up for, said Khan.
Other long-term adverse effects of keto include digestive issues like constipation, bloating, and diarrhea, and a higher risk of kidney stones.
The Best Way to Do Keto
The contradictory findings point to one conclusion: More research, especially long-term, is needed to make sure the keto diet is safe. So far, it seems that the short-term benefits may not offset the long-term risks.
With that in mind, the safest way to make the most of keto may be to take breaks from time to time.
A 2024 study found that sticking to a continuous ketogenic diet might age cells – especially in your heart and kidneys – potentially leading to harmful inflammation. But people in the study who took breaks from the diet didn't have these negative effects.
"The biggest thing we tried to stress is you don't want to be on it for too long," said study author David Gius, MD, PhD, a professor of radiation oncology at University of Texas Health San Antonio. "Take a break. Take a keto vacation."
That means following a keto diet for about four to five days, long enough for most people to enter a state of ketosis, followed by a break of two to three days.
But that's not the only precaution to take, Gius said.
You also need to talk to your doctor and a dietitian before trying keto, as the diet must be tailored to each person, he said. Ask your doctor for a lipid panel and heart panel, along with a thorough cardiac exam, said Gius, who recommended checking back in every three to six months for updated lipid and heart panels.
"Other than the rise in LDL cholesterol, I think keto is safe," said Weiss. He recommends a hybrid model approach: a low-carb, Mediterranean-style diet rich in fruits, vegetables, whole grains, and heart-healthy fats and low in processed foods. Several randomized clinical trials link this eating pattern to a lower risk of chronic diseases, longer lifespan, and the prevention of conditions like heart disease, type 2 diabetes, atrial fibrillation, and breast cancer.