Today, the diet has become trendy, and many people are using it to lose weight. However, eating high levels of saturated fat may pose a risk for long-term heart health — and in the short term, severely low carb diets may come with unpleasant side effects, like constipation and headaches, notes the Mayo Clinic. Given the restrictive nature of keto (it eliminates most fruit and dairy, whole grains, many vegetables, and legumes), you may also fall short in terms of certain nutrients, like fiber.
2. Is the Keto Diet Safe to Follow?
Even though following an extremely high-fat diet can feel like a radical way to eat, “the research looking at ketosis via diet has not shown any real negative consequences when done in the short term,” says Scott Keatley, RDN, of Keatley Medical Nutrition Therapy in New York City. (Ketosis is the natural metabolic state in which your body is burning fat instead of its usual fuel source, glucose, which is a kind of sugar.) But there have been few long-term studies, adds Kendra Whitmire, CNS, who practices functional and therapeutic nutrition in Laguna Beach, California. It’s difficult to definitively say that it’s safe, and it also largely depends on the types of foods you’re eating on the diet. (For instance, olive oil is a healthier choice than butter; salmon is healthier than bacon.) That said, following the keto diet properly, and particularly with help from a medical professional, should reduce negative health effects, says Whitmire. RELATED: What Are the Benefits and Risks of the Keto Diet?
3. Is Ketosis Bad?
Typically, your body breaks down carbohydrates as its preferred fuel source. Ketosis is when your body has switched into a fat-burning state and breaks down fat into ketone bodies that are used as energy. Beyond the keto flu, “many studies have shown that entering ketosis via diet does not have any real negative consequence in the short term,” says Keatley. But long-term studies are needed to truly assess the impact, he adds. Bottom line: Putting your body into ketosis for a limited time is likely not harmful for most healthy people. RELATED: Should You Use Exogenous Supplements to Put Your Body in Ketosis?
4. How Many Carbs Do You Actually Eat on a Keto Diet?
A keto diet is generally made up of 70 to 75 percent fat, 20 to 25 percent protein, and 5 to 10 percent carbohydrates, says Jill Keene, RDN, a registered dietitian nutritionist in private practice in White Plains, New York. The exact number of grams (g) of carbohydrates will be different for everyone, but it is generally around 20 to 50 g per day. Many people on a keto diet count “net carbs,” which is total carbs minus fiber. Fiber isn’t “counted” in the carbohydrate total because it doesn’t get digested by the human body. Either way, that number of carbs is very low and requires careful planning. Eating a little fruit, starchy vegetables, sugary foods, or whole grains can easily kick you out of ketosis.
5. Can You Drink Alcohol on the Keto Diet?
Yes. “Even though there are often carbs in alcohol, you can still drink it in limited amounts,” says Keatley. Realize that on days when you do choose to consume alcohol, you may have to adjust your carbs from other sources, depending on the kind of alcohol you have. That may mean making tough decisions, like having a drink but skipping a small amount of fruit or Greek yogurt. Spirits (enjoyed straight, without mixers) tend to be the most keto-friendly alcohol, followed by wine. You may want to halve your usual serving, says Keatley. Beer and wine can eat up a lot of your carbs, and they don’t give back in terms of vitamins and minerals. “It’s a waste of your carbs,” he says. Here’s what each alcoholic drink contains, carb-wise, according to the U.S. Department of Agriculture (USDA):
Spirits: gin, rum, vodka, whiskey, 1.5 fluid ounces, 0 g carbs (1 serving)Red wine, 5 fluid ounces, 4 g carbs (1 serving)White wine, 5 fluid ounces, 4 g carbs (1 serving)Light beer, 12 fluid ounces, 6 g carbs (stick to half of a beer if this is your choice)
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6. How Much Weight Can You Lose on the Keto Diet?
There’s no doubt that a ketogenic diet may help spur weight loss, at least initially — and anecdotal reports of drastic transformations are easy to find. “I have clients who have lost a significant amount of weight on a keto diet, but they were obese when starting and had quite a bit of fat to lose. These individuals can have fairly drastic body transformations,” says Keatley. In a study published in 2017 in the Journal of Clinical Endocrinology, 20 people with obesity who followed a very low-calorie keto diet for four months lost an average of 44 pounds, mainly from body and visceral fat. (It’s important to note that there was no placebo group and this was a small sample source, so the findings are limited, and the diet followed included just 600 to 800 daily calories, which is well below what most health professionals recommend.) In another study published in 2017, in Nutrition Metabolism, normal-weight adults who followed a non–energy (calorie) restricted keto diet for six weeks lost about 4 pounds in both fat and lean body mass. But long-term studies show that there’s not much of a difference in weight loss between keto and other diets. A past meta-analysis compared adults on a ketogenic diet (eating less than 50 g of carbs) with those on a conventional low-fat diet. After at least a year, those on the keto diet lost an additional two pounds, compared with the group that slashed fat. The bottom line is that many diets, including keto, may help you lose the same amount of weight in the long run. With that news, know that there may be a better option out there for you, says Keatley. RELATED: 21 Tips for Weight Loss That Actually Work
7. What Fruits Can I Eat on the Ketogenic Diet?
Fruit is generally not a mainstay of the keto diet. With so much natural sugar, fruit generally has too many carbs to be included. But you can have small amounts of lower-carb fruits, like berries, says Whitmire. And if you’re really getting technical, avocado and coconut, two higher-fat foods, are, in fact, fruits. Based on USDA carb counts*, here are the fruits that can work on a keto eating plan:
Raspberries: 3 g net carbs per ½ cupStrawberries: 2.5 g net carbs per ¼ cup slicedBlueberries: 4.5 g net carbs per ¼ cupBlackberries: 3 g net carbs per ½ cupCoconut: 2.5 g net carbs per ½ cup, shredded, raw (unsweetened)Avocado: 3 g net carbs per 1 cup, cubed
*All carb values are net carbs, which is total carbs minus fiber. Fiber is often not counted in net carb totals, as the nutrient doesn’t get digested.
8. Can I Eat Snacks Like Popcorn, Oatmeal, and Yogurt on Keto?
Unfortunately, high-carb foods like popcorn or oatmeal probably won’t fit in the keto diet. One cup of air-popped popcorn contains 5 g of net carbs, per USDA data, which may be a quarter of your carb allotment for the entire day. It’s also worth mentioning that 1 cup of popcorn is not a large serving; it contains just 30 calories and no fat, so it won’t be filling. Oatmeal likely doesn’t fit either. About a quarter cup of plain dried oats (about half a cup cooked, also a small portion) has 12 grams of net carbohydrates for 77 calories and just 1 gram of fat, per the USDA. As for yogurt, it depends on what type you choose and whether it’s keto-compliant. One 5.3-ounce container of Fage plain 5 percent milk fat Greek yogurt, for instance, contains 5 g of carbohydrates. Remember to choose plain versions, as flavored ones will add more sugar (and, therefore, carbs). Better keto-compliant snacks include nuts (1 ounce of almonds has 3 g net carbs, per USDA data), seeds (half a cup of sunflower seed kernels has 3 g of net carbs), and small amounts of low-carb fruits like berries, says Whitmire. Beef jerky and nonstarchy veggies such as broccoli and cucumbers are other good snack options on keto. RELATED: 10 Quick and Easy Keto Snacks Probably Already in Your Fridge or Pantry
9. Should I Be Concerned About the Keto Flu?
If you’re interested in the keto diet, you have probably read about the keto flu, one not-so-fun side effect. “The keto flu is definitely real,” says Keatley. “Your body functions really well on carbohydrates — that’s what it was designed for. When it switches to fat burning, it becomes less efficient at making energy,” he says. On keto, you have less energy available and you may feel sick and sluggish, kind of as if you have the flu. As your body naturally adjusts to this new way of drawing energy, you will come out of it. This may take a couple of weeks, says Keatley.
10. Will the Keto Diet Give Me Kidney Stones?
“Consuming high levels of red meat and not drinking a lot of water may make stones more likely,” says Whitmire. She adds that on a keto diet, you need to stay hydrated and replenish electrolytes (minerals like sodium, potassium, magnesium, and calcium). “If not, this can increase your risk of side effects like stones,” she says. Past research gives a small glimpse into how likely kidney stones may be. A systematic review and meta-analysis published in 2021 in Diseases found that adults who follow the keto diet have a slightly elevated risk of developing kidney stones. If you have risk factors, like a family or personal history of stones, talk to your doctor about any precautions you should take when on the keto diet. RELATED: The Short- and Long-Term Effects to Expect on the Keto Diet
11. How Might the Keto Diet Affect My Period?
There’s a possibility you may see a change in menstruation. “Studies on younger women who eat severely low-carb for an extended period of time end up with irregular periods or missed periods,” explains Whitmire. Severely limiting carbohydrates may be taxing on the adrenal system, leading to hormonal imbalances that disrupt a woman’s cycle. Similarly, rapid weight loss can also have this effect. The takeaway? “Women may need more carbs on a keto diet compared to men, especially if a woman is noticing a change in her cycle,” she adds. On the other side of the spectrum, there is limited evidence that for women with polycystic ovary syndrome (PCOS), a ketogenic diet may improve their hormonal balance. A small study, published in Nutrition & Metabolism, found that a small group of women with PCOS who followed a keto diet for 24 weeks lost 12 percent of their body weight and reduced testosterone and insulin levels. Again, talk to your doctor, especially if you’re using the diet as part of your treatment.
12. How Long Do You Need to Stay on the Keto Diet to Lose Weight?
Anecdotally, many people report losing weight quickly on a keto diet, says Keatley. Research in the Journal of Clinical Endocrinology found that obese dieters lost an average of 44 pounds over four months when following a very low-calorie keto diet. That said, Keatley suggests to clients that they spend no more than 12 weeks in ketosis because of the uncertainties of following it long-term and the risk of developing nutritional deficiencies. When people go off a keto diet and begin to incorporate more carbs into their day, they tend to regain some weight during the adjustment period, he says. They also stand to regain all the weight they lost, and potentially more, if they return to their pre-keto ways of eating after feeling deprived on the plan. RELATED: The 10 Most Famous Fad Diets of All Time
13. How Will the Keto Diet Affect Your Cholesterol Levels?
The interesting thing about a keto diet is that it often leads to weight loss, something that by itself can improve blood lipid levels. At the same time, you may be consuming more saturated fat than ever, in the form of butter, bacon, cream, and coconut oil. We’ve long been warned that eating excess saturated fat can raise cholesterol and thus put us at risk of heart disease. For that reason, many experts express concern that increased fat intake may be especially harmful for people who already have heart disease or have risk factors for it. A small study of obese patients on a keto diet found that after 24 weeks, total cholesterol levels dropped, while “bad” LDL cholesterol decreased and “good” HDL cholesterol increased. That could be reflective of the fact that any weight loss, no matter how it is achieved, tends to lower cholesterol. Also, as already mentioned, people who have risk factors for heart disease need to consult their doctors before attempting a keto diet. Past research has concluded that a diet low in carbs but high in fat and protein impaired arterial function in those who were at risk of cardiovascular disease. What it may come down to is what type of fat you’re consuming on keto. A review and meta-analysis looked at the effect of a low-fat diet versus a low-carb diet on blood lipids. While lower intakes of saturated fat were associated with lower cholesterol levels, higher intakes of monounsaturated fat (like olive oil or avocado) in the context of a high-fat diet were associated with increased levels of heart-protective HDL cholesterol.
14. How Much Protein Will You Eat on the Keto Diet?
A typical keto diet may include 20 to 25 percent of calories coming from protein, says Keene. One common misconception is that this is a high-protein diet, when in reality it’s moderate in protein. “Too much protein can be converted and broken down as sugar to be utilized as an energy source,” she says. That will kick the body out of ketosis. That said, you don’t want to go too low in protein. “You want to be able to stay in ketosis without sacrificing lean body mass (muscle) if you lose weight,” says Whitmire. This can loosely equate to 1.2 to 1.5 g of protein per kilogram of body weight. (The recommended daily allowance is currently 0.8 g per kilogram of body weight, according to Harvard Health Publishing.) Therefore, a 140-pound woman may aim for 76 to 95 g per day. For reference, a 3-ounce chicken breast offers 26 g of protein, according to the USDA. One of the best sources of protein on a keto diet is fatty fish (like salmon or mackerel), says Keene, as it offers a source of heart-healthy protein and omega-3 fatty acids. Eggs are another good choice; one large egg contains 6 g of protein and 5 g of fat. While a keto diet may focus on fat, that doesn’t mean you have to eat bacon and sausages all day. There is room for leaner proteins, like chicken or cod; just remember to add fat (for example, roast the chicken with olive oil) to these lower-in-fat sources, she says. Many cuts of beef are also considered lean or extra lean, as they contain 10 g or less of total fat, as well as a modest amount of saturated fat (4.5 g and 2 g or less, respectively). These include eye of round roast and steak, sirloin tip side steak, top round roast and steak, bottom round roast and steak, and top sirloin steak, notes the Mayo Clinic. RELATED: What Is Keto Cycling and Can It Help You Stick With the Keto Diet?
15. Can the Keto Diet Reverse Type 2 Diabetes?
“Though this isn’t the first tool I’d use to help someone control their insulin — carb counting, evenly distributing carbs throughout the day, may be easier to commit to — it’s not off the table, especially with stronger emerging research,” says Keene. It’s true: Some preliminary research suggests keto may be a good approach for some people with type 2 diabetes. For example, a small study published in 2017 in the Journal of Medical Internet Research randomized overweight adults with type 2 diabetes into two groups: one that consumed a keto diet, and a control group that ate a low-fat diet recommended by the American Diabetes Association. After 32 weeks, the keto group saw their A1C (a measure of average blood sugar over a three-month span) fall more, compared with the control group, and half lowered their A1C to less than 6.5 percent (less than 5.7 percent is considered normal). The keto group also lost 28 pounds, compared with about 7 pounds for the control group. But larger and longer-term studies are needed, and keto can pose health risks to people with diabetes, especially if you’re following it without supervision from a medical professional. Importantly, anyone who is on medication to lower blood sugar or who is using insulin should be aware that drastically cutting carbs, as you must do on keto, can lead to dangerously low blood sugar, research shows. Unaddressed, this condition, called hypoglycemia, may lead to seizures, loss of consciousness, and blurred vision, according to the Mayo Clinic. (People with type 1 diabetes should not try the keto diet, experts warn.) The takeaway? Be sure to work with your doctor if you have type 2 diabetes, and manage your expectations. Not only is there no consensus about whether keto is an effective diet approach for diabetes, it’s also tough to stick with, according to research published in the European Journal of Nutrition in 2018. Keep in mind that type 2 diabetes cannot be reversed, but it can be put into remission.
