What to Expect on Keto: The Short- and Long-Term Effects of the Ketogenic Diet

This high-fat, very low carb way of eating can be tough to tackle, but it’s gaining in popularity. Here are the possible short- and long-term effects of the diet.

Medically Reviewed
While studies suggest the keto diet can lead to quick weight loss, long-term effects of the diet fad are less clear.Thinkstock

The keto diet may be the most buzzed-about eating plan of  the moment, but it’s no walk in the park. Essentially, when following a keto diet food list, you’re eating mostly keto-friendly fat (60 to 80 percent of your calories) and very low carbohydrates, starting with 20 to 30 grams (g) per day. This allows your body to use fat for energy rather than carbohydrates, sending you into a state called ketosis.

While fans talk about the amazing weight loss results you may see from cutting so many carbs, there’s one vital truth to keep in mind: “It’s very important to understand that the ketogenic diet doesn’t work the same for everyone,” says the New York City–based dietitian Kristen Mancinelli, RD, author of The Ketogenic Diet: A Scientifically Proven Approach to Fast, Healthy Weight Loss.

Your unique body chemistry dictates how you'll respond to eating this way, but there are some universal truths. Here’s what you can and can’t expect to happen on the diet, including the possible benefits and risks of keto!

What the Keto Diet Can Do for Your Health

You’ll slim down if you try the keto diet — and it’ll probably be fast. “When a person goes on a keto diet, they lose a lot of weight. That’s just what happens,” says Mancinelli. Indeed, a review found that the keto diet was effective in spurring weight loss and improving cardiovascular health risk factors. (1)

Your metabolism may increase slightly from keto, says Mancinelli, but the weight loss benefits derive more from the fact that you likely won’t be as hungry. “Are you really going to sit down and eat three avocados and an entire roast chicken? Nope. You won’t be eating the same number of calories because you won’t want to eat that much,” she says. The ketogenic diet may help decrease your appetite.

What the Keto Diet Can’t Do for Your Health

But the keto diet won’t fix all your health woes. Another study points out that the health benefits are controversial. (2) Some animal research points to potential problems like nonalcoholic fatty liver disease from long-term adherence to the diet. Even though these are animal studies, they do point toward the need for more research into implications of the diet. You shouldn't think of this diet as something you’ll do for the rest of your life.

The diet also doesn’t get rave reviews from US News & World Report, which relies on a panel of medical experts to rank 41 diets. Coming in at No. 38 in the 2019 list of Best Diets Overall, the keto diet received lower marks compared with other plans, like the Mediterranean diet, because of conflicting research on whether keto helps or harms people with heart conditions or type 2 diabetes. Consumption of foods like fruit and whole grains is correlated with heart health and diabetes prevention, and the keto diet cuts these out.

The keto diet may be dangerous if you have certain health conditions, like kidney disease. The panel also remarked that it’s extremely difficult to follow.

What Are the Possible Short-Term Effects of the Keto Diet?

In the beginning, you’ll have to go very low in carbs, around 20 to 30 g a day, to ensure your body goes into ketosis, advises Mancinelli. (Some people call a keto diet anything that limits carbs to less than 50 g a day, though there are various types of keto.) And that can be difficult. When you’re eating a high-fat and very-low-carbohydrate diet, you’re eliminating many foods, including fruit, most dairy, starchy veggies, whole grains, and legumes (and certainly all sugar). It’s difficult and at times uncomfortable.

In the short term, before you begin to lose weight, you may also experience what people call the keto flu, a state that lasts about a week as your body adjusts to the diet. That can include extreme fatigue and foggy-headedness. (Not everyone feels this, Mancinelli allows.) Knowing that keto flu is a possibility can help you plan the best time to start the diet. You can also mentally prepare for this transition period — reminding yourself that it’s only temporary can help immensely.

For these reasons, “some people won’t be able to stay on it,” says Mancinelli. You should aim to give it at least six weeks. After that, if you feel exhausted or hate eating the food, then the diet is probably not for you. However, if you feel energetic after keto flu symptoms subside within a couple of weeks, which some people report, you may see success with the plan.

What Are the Possible Long-Term Effects of the Keto Diet?

“I don’t recommend staying on the keto diet permanently. It can be really restrictive,” says Mancinelli.

Long-term research on the keto diet is limited, so there’s no telling for sure what cutting out certain major food groups and cutting carbs will eventually do to your body. Registered dietitians warn that nutrient deficiencies may be possible if you’re on it for too long.

Stick to the keto diet for three to six months max, says Mancinelli, noting that some people opt to cycle in and out of the diet throughout the year.

Because it’s not a forever diet, there will be life after keto. But even when you go off it, you can expect that your taste preferences will have changed. “You likely won’t want as many carbs, and things will taste extremely sweet,” she says. That’s good, because the last thing you want to do is go back to your old eating habits and regain weight that you lost.

While everyone’s nutrition requirements differ, generally, you may eat 40 to 45 percent fat and stick to 120 to 150 g of carbs per day to help you keep the weight off, she says. That said, the US News report noted that the long-term weight loss effects of keto aren’t clear.

The Takeaway: What to Expect if You Try the Ketogenic Diet

The ketogenic diet isn’t a miracle diet for weight loss or a fix for all health problems. For certain people (like those with kidney disease), it can be dangerous. And because it’s not a long-term plan, you have to manage your diet carefully after stopping keto.

Think about how your lifestyle fits with such a restrictive plan, as well as what you’re willing to give up temporarily (like eating the same foods as your family). Let that be your guide to help you determine if the keto diet is right for you.

Editorial Sources and Fact-Checking

  1. Paoli A. Ketogenic Diet for Obesity: Friend or Foe? The International Journal of Environmental Research and Public Health. February 2014.
  2. Kosinski C, Jornayvaz ER. Effects of Ketogenic Diets on Cardiovascular Risk Factors: Evidence From Animal and Human Studies. Nutrients. May 2017.
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