Following the ketogenic diet means sticking to a high-fat, moderate-protein, low-carb meal plan. What’s the purpose? Eating this way puts your body in a state of ketosis, so you burn fat rather than sugar for energy.
Though it wasn’t developed as a weight-loss plan, that’s what keto has become, with hordes of devotees dedicated to obtaining most of their calories from fat and protein and limiting themselves to less than 50 grams of carbs a day. While fans rave about the pounds they’ve shed, health experts say there are some potential drawbacks to the keto diet, such as a loss of muscle mass, diarrhea, and a condition dubbed the keto flu.
Another downside to keto is that you could become deficient in some crucial nutrients that are typically found in foods banned or restricted under keto guidelines. If you follow keto or are thinking about trying it, nutritionists say you should consider taking these five supplements to make up for the nutrients you might miss.
Many high-magnesium foods, like whole grains, bananas, and beans, are not keto-friendly because they contain too many carbs per serving, explains Seattle-based nutritionist Ginger Hultin, RD, a spokesperson for the Academy of Nutrition and Dietetics.
“Magnesium is a mineral that’s important for many cellular functions and helps regulate nerves, muscles, and the immune system,” Hultin says. It also plays a role in building strong bones, maintaining blood sugar levels, and keeping your heartbeat steady. “It is critical for the body to make protein, bone, and DNA, too,” she adds.
Keto devotees can try to meet their recommended intake of magnesium (310 to 320 mg, depending on your age) by consuming keto-approved, magnesium-rich foods like spinach, broccoli, kale, pumpkin seeds, and sunflower seeds. But taking a magnesium supplement can make sure you cover your bases. “Talk to your doctor about possible supplementation but be sure not to exceed the recommendations, as too much magnesium can cause diarrhea,” says Hultin.
Many milk and dairy products don’t work on the keto diet because of their carbohydrate levels—think whole milk or flavored yogurts, both of which have 12 grams of carbs per serving. (Remember, keto followers are advised to limit carb intake to under 50 mg daily.) By largely limiting or avoiding milk products, you also limit your intake of calcium. Depending on your age, women should take in 1,000 to 1,300 mg of calcium daily.
“Calcium is a mineral that helps maintain bone health but also supports muscle and nerve communication,” says Hultin. “It helps the cardiovascular system and supports the release of hormones.” Other foods with optimum levels of calcium that are excluded or limited on keto include fortified orange juice and tofu. “The good news is that you can get calcium from sardines with bones, salmon with bones, kale, and broccoli,” she says.
Yet if you find it hard to eat so many leafy greens or you dislike fish, that’s where a calcium supplement comes in. “Talk to your doctor about how much calcium you may need to supplement with based on your diet and your needs,” she advises.
Think of iron as the fuel that allows every cell in your system to function properly. “Iron is a mineral the body needs to make hemoglobin, a protein in red blood cells that carries oxygen throughout the body,” says Hultin. Without the 18 mg of iron recommended daily for non-pregnant women between ages 18 and 50, you’ll feel lethargic and weak, and your skin may appear paler.
Many keto-approved foods contain excellent amounts of iron, says Hultin, such as beef, some fish, and oysters. However, other solid iron sources are restricted or excluded from the keto diet, like fortified breakfast cereals, lentils, tofu, and beans, she says.
Getting adequate iron is even more challenging if you are a vegetarian or vegan on keto, since you can’t consume animal products. Leafy greens, like kale and spinach, are good plant sources of iron, but the type of iron they contain is not easily absorbed by the body. To ensure that you’re getting the right amount, a daily iron supplement is a smart idea. Make sure you try to meet your needs through the diet, and check with your doctor if you may need supplementation,” says Hultin.
Getting sufficient amounts of vitamin D is hard even if you’re not on keto. The sunshine vitamin is made by the body when skin is exposed to the sun—and direct sun exposure is something many people try to avoid to lower the risk of skin damage and skin cancer. Though vitamin D is also found in some foods—such as milk, orange juice, and cereal—these items are limited under keto because of their high carb counts.
But vitamin D is essential. “Vitamin D is necessary for bone health, and being deficient for a long period of time can lead to the development of brittle bones and fractures,” says New York City nutritionist Natalie Rizzo, RD. It gives you energy, powers your immune system, and may even help ward off depression.
To get your recommended daily intake (600 IUs), you could turn to keto-approved fatty fish such as salmon and tuna, or up your intake of eggs—a keto favorite thanks to the high-fat yolk. But with so few food options, a daily vitamin D supplement can come in handy. Check with your physician for the right amount based on your needs.
You need fiber to keep your GI tract running smooth and to avoid digestive buzzkills like constipation. But most sources of fiber come from carbohydrate-rich bread, grains, fruits, and vegetables, and these are not keto-friendly.
“Since these foods are limited on the keto diet, so is your intake of fiber,” explains Rizzo. When you lack fiber, it opens the door to other health risks too, such as obesity, heart disease, and a higher risk of developing colon cancer, she says.
“Because you can eat some carbs on keto, you should opt for fiber-rich veggies, such as broccoli and cauliflower,” she advises. But since it would be tough to fill your entire diet with these day after day, a daily fiber supplement could be a big help. Rizzo suggests talking to your doctor about the best one for you and how much to take. You don’t consume too much and end up with loose stools or diarrhea, she warns.