The appeal of this diet is clear—you’re encouraged to eat delicious, high fat foods like hard cheese, butter, bacon, steak, and even bun-less burgers in copious amounts. The key is very low carbohydrate intake and high fat consumption, so that your body is forced to burn stored fat for fuel instead of carbs.
But is the ketogenic diet good for you? According to a report from the American Heart Association, not so much. In fact, keto ranked as one of the unhealthiest. The report categorized popular diets into four tiers, and keto was placed in tier four—the lowest.
Why? Because it restricts food groups considered essential for a heart-healthy diet and instead promotes high saturated fat sources that are strongly discouraged.
Basics of keto
Burning fat is considered an ideal way to lose weight. The basic breakdown of keto involves consuming less than 10 percent of calories from carbohydrates and more than 70 percent of calories from fats, says Kristina Petersen, nutritional sciences professor at Texas Tech University. What this looks like is generally a lot of animal-derived foods and fewer plant-based items.
“The way the body normally works is that it uses glucose or carbohydrate as its main source of energy,” Petersen says. “When you go on a ketogenic diet and you're restricting carbohydrate intake, the body adapts, and so the body uses the fat that you're consuming to derive energy. The problem is not all cells can use fats for energy, so this is where ketones are formed.”
Weight loss is the most common reason to go keto, says Maya Vadiveloo, a nutrition and food sciences professor at the University of Rhode Island. From a behavioral standpoint, it can be appealing for people trying to lose weight quickly to choose a diet with more black-and-white rules and completely cut out entire food groups rather than think about the nuances of complex carbs and appropriate portion control, she says. But these restrictions that can sometimes be helpful for short-term weight loss often backfire because it's not something that can be adhered to long-term.
How the keto diet leads to weight loss
The body stores a certain amount of protein, fat, and carbohydrates, to use as fuel during periods of fasting. That balance gets replenished every time you eat, but once the stored carbohydrates—which are essential for brain function—are depleted, the body can use fat to create molecules called ketones as the preferred energy source.
Ketones are chemicals that the body produces when it starts breaking down fat for energy. When ketones are present, the body transitions into a metabolic state called ketosis. People sometimes experience lethargy, dry mouth, or feeling overall unwell, when they start the diet—symptoms of ketosis dubbed the “keto flu.” But once your body adapts, those symptoms will usually dissipate.
For the body to remain in ketosis, carbohydrate intake must be reduced to 10 percent, which means restricting a lot of food groups. Grains, fruits, non-starchy vegetables, many dairy products, and even certain nuts contain carbohydrates and therefore must be limited. Consuming large amounts of higher fat dairy and fattier cuts of meat is common to achieve these nutritional goals.
The healthier way to follow keto would be choosing mostly plant-based sources of fat, like avocados, nuts, and oily fish versus fatty red meat. However, that can become even harder to maintain since many of those sources also contain carbohydrates.
“While it may be possible for some people to adhere to it in a healthier way, the more restrictions you have on food groups, the more difficult it is to adhere to, so I think it's not as likely that, long-term, that people will consume only heart-healthy oils,” Vadiveloo says.
The worst of popular diets?
Even if you can manage keto in an optimal way, you’re still going to be missing out on opportunities to consume the healthy phytochemicals and fiber from whole grains, fruits, and vegetables.
So far, there are not yet any long-term studies that reveal the health implications for people following the keto diet.
“Based on what we know about this diet, the foods that are included and emphasized, the foods that are limited, we do speculate that it would be associated with higher risk of cardiovascular disease,” says Petersen, who contributed to the recent American Heart Association (AHA) report. “And we know in the short-term studies done on the ketogenic diet that people do have elevations in blood cholesterol levels, which is a key risk factor.”
According to Petersen, whole grains have been shown to lower blood cholesterol levels, and fruits and vegetables are proven to be good for blood pressure. All these foods are associated with lower risk of cardiovascular disease long-term.
“Additionally, I would say that if people are not consuming a large portion of non-starchy vegetables, they might have inadequate amounts of fiber, which increases different cancer risks as well as cutting into the positive effects on cholesterol management,” says Vadiveloo, who also contributed to the AHA report.
Is keto good for people with diabetes?
Certified nutritionist Maya Feller says that many of her clients want to do keto to lose weight quickly, and because they believe that their A1C—a blood test that measures average blood sugar levels—will drop, which may be beneficial for those with pre-diabetes or diabetes. The challenge is that it also raises the LDL, or low-density lipoprotein cholesterol, which raises the risk for heart disease and stroke.
“If you have someone who has diabetes, then we're also thinking about their entire vasculature and so I don't want to suggest something that in the long term is harmful, and would possibly promote plaque buildup, which will definitely have an impact on their endocrine system,” she says.
Which brings us to the question of who can benefit from this diet?
As far as the experts are concerned, the answer is no one. Peterson says that when you look at evidence-based guidelines, it doesn't appear as a recommendation for any disease or treatment aside from drug resistant epilepsy (which was the original purpose of the diet).
A classic ketogenic diet is not advised for people with diabetes, though lower carbohydrate intake may be. That could involve lowering to somewhere between 20 and 40 percent of calories from carbohydrates to help with blood glucose management, as opposed to the 10 percent required for keto.
“I think there are more trade-offs than benefits there,” Vadiveloo says.
Feller believes the real challenge is that nutritional literacy levels are quite low for the average person in this country. People don’t really know what a protein, fat, or carb is and how to consume them in helpful ways for their individual constitution. They may not understand that not all carbohydrates are the same, or that they can serve a useful purpose.
The AHA report clarifies that there are healthier and less healthy ways to follow all popular dietary patterns, and nutrition misinformation, misplaced emphasis, or oversimplification may lead to adoption of patterns not as intended. Feller feels the entire paper was largely a response to the misinformation she sees spreading over social media.
While we don’t have conclusive scientific studies to lay out the exact long-term implications of the ketogenic diet, we do know that the nature of the diet does not comply with AHA guidelines for heart health and that experts do not recommend it for the general population. Everybody is different, but if you’re considering keto, it may be best to speak with your doctor first.