Written By: Jessica Migala

“In terms of diabetes, there is some promising research showing that the ketogenic diet may improve glycemic control. It may cause a reduction in A1C — a key test for diabetes that measures a person’s average blood sugar control over two to three months — something that may help you reduce medication use,” she says.

But for people with diabetes, one big concern is you're eating a lot of fat on keto, and that fat may be saturated, which is unhealthy when eaten in excess. (The much higher total fat intake is also a challenge among keto beginners.)

Because people with type 2 diabetes are at an increased risk for cardiovascular disease, there’s a specific concern that the saturated fat in the diet may drive up LDL, or “bad,” cholesterol levels, and further increase the odds of heart problems. If you have type 2 diabetes, talk to your doctor before attempting a ketogenic diet. She may recommend a different weight loss diet for you, like a reduced-calorie diet, to manage diabetes. Those with epilepsy should also consult their doctor before using this as part of their treatment plan.

The keto diet may also help improve short- and long-term cognition among people who are living with Alzheimer’s disease and are experiencing mild cognitive impairment, according to a systematic review of randomized controlled trials that was published in Advances in Nutritionin June 2020. Researchers caution that further research is needed to confirm these findings and prove a cause-and-effect relationship between keto and preventing dementia.

In terms of weight loss, you may be interested in trying the ketogenic diet because you’ve heard that it can make a big impact right away. And that may be true. “Ketogenic diets will cause you to lose weight within the first week,” says Mattinson. She explains that your body will first use up all its glycogen stores (the storage form of carbohydrate). With depleted glycogen, you’ll drop water weight. While it can be motivating to see the number on the scale go down (often dramatically), do keep in mind that most of this is water loss initially.

But the keto diet can be an effective option over time. One review suggested the keto diet can spur fat loss in obese people when used for a couple of weeks and up to one year. A meta-analysis noted that one likely reason for weight loss is that keto diets may suppress hunger.

One downside to the ketogenic diet for weight loss is that it's difficult to maintain. “Studies show that weight loss results from being on a low-carb diet for more than 12 months tend to be the same as being on a normal, healthy diet,” says Mattinson. While you may be eating more satiating fats (like peanut butter, regular butter, or avocado), you’re also way more limited in what’s allowed on the diet, which can make everyday situations, like eating dinner with family or going out with friends, far more difficult. Because people often find it tough to sustain, it’s easy to rely on it as a short-term diet rather than a long-term lifestyle.

Another potential downside to the keto diet: the keto flu. One study, published in March 2020 in Frontiers in Nutrition, found that across 43 different online forums for people following a keto diet, about a third of commenters reported experiencing this short-term keto side effect. In the first few days after you begin your keto diet plan, you may experience headaches, muscle cramps, fatigue, nausea, constipation, and other flu-like symptoms, according to Harvard Health Publishing. These symptoms usually resolve within a few days to a few weeks, and you can help to counter them by drinking plenty of fluids with electrolytes, according to an article published June 2020 in StatPearls.

Before starting, ask yourself what is really realistic for you, Mattinson suggests. Then get your doctor’s okay. You may also work with a local registered dietitian nutritionist to limit potential nutrient deficiencies and talk about vitamin supplementation, as you won’t be eating whole grains, dairy, or fruit, and will eliminate many veggies. “A diet that eliminates entire food groups is a red flag to me. This isn’t something to take lightly or dive into headfirst with no medical supervision,” she says.