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The ketogenic diet is a high-fat, moderate-protein and very low-carbohydrate diet. Carbohydrates are the body's preferred source of energy, but on a strict ketogenic diet, less than 5 percent of energy intake is from carbohydrates. The reduction of carbohydrates puts the body into a metabolic state called ketosis. Ketosis is when the body starts breaking down stored fat into molecules called ketone bodies to use for energy, in the absence of circulating blood sugar from food. Once the body reaches ketosis, most cells will use ketone bodies to generate energy until you start eating carbohydrates again.
Traditionally, the ketogenic diet was only used in clinical settings to reduce seizures in children with epilepsy. "Now there is a lot of interest in the diet's effectiveness in helping with other neurological conditions, cancer, diabetes, PCOS [polycystic ovary syndrome], obesity, high cholesterol and cardiovascular disease," says Emily Stone, M.S., R.D. People also eat keto to lose weight.
Related: Ketogenic Diet 101
"There is solid evidence to support use of the ketogenic diet in individuals with epilepsy who have seizures that are drug resistant," says Laura Dority, M.S., R.D., L.D., with Keto Knowledge LLC. In the short term, people who follow the diet report weight loss. Dority says, "There is certainly some good recent research showing promise in disorders such as autism, traumatic brain injury, brain tumors, migraines and Alzheimer's (to name a few but the list could go on), as well as some great research on ketogenic diets and type 2 diabetes reversal including dramatically reducing insulin needs, fasting blood sugar levels, lowering A1C and obtaining significant weight loss."
"Like most highly restrictive diets, it is difficult to meet nutritional needs while doing keto," says Stone. "It often comes with uncomfortable side effects like constipation and the 'keto flu.' Also, the long-term health consequences are not well understood."
Another con of the ketogenic diet is that it is confusing to know what you can and cannot eat. We break it down here.
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Here is a list of all the low-carb foods that are appropriate to eat when you're following keto.
Fish is rich in B vitamins, potassium and selenium; it's also protein-rich and carb-free. Salmon, sardines, mackerel, albacore tuna and other fatty fish boast high levels of omega-3 fats, which have been found to lower blood sugar levels and increase insulin sensitivity. Frequent fish intake has been linked to a decreased risk of chronic disease as well as improved mental health. Aim to consume at least two 3-ounce servings of fatty fish weekly.
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Nonstarchy vegetables are low in calories and carbs, but high in many nutrients, including vitamin C and several minerals. They also contain antioxidants that help protect against cell-damaging free radicals. Aim for nonstarchy vegetables with less than 8 g of net carbs per cup. Net carbs are total carbohydrates minus fiber. Broccoli, cauliflower, green beans, bell peppers, zucchini and spinach fit the bill.
Cheese has zero carbohydrates and is high in fat, making it a great fit for the ketogenic diet. It's also rich in protein and calcium. But, a 1-ounce slice of cheese delivers about 30 percent of the daily value for saturated fat, so if you're worried about heart disease consider portions when noshing on cheese.
Yogurt and cottage cheese are high in protein and calcium-rich. Five ounces of plain Greek yogurt provides just 5 g of carbohydrates and 12 grams of protein. The same amount of cottage cheese also has 5 grams of carbohydrates with 18 grams of protein. Studies have shown that both calcium and protein can reduce appetite and promote fullness. Higher-fat yogurts and cottage cheese help keep you full for longer, and full-fat products would be part of the ketogenic diet.
Choose heart-healthy fats like avocados, which are high in monounsaturated fat and potassium, a mineral many Americans are lacking. Half of a medium avocado contains 9 grams of total carbohydrates, 7 grams of which are fiber. Swapping animal fats for plant fats like avocados can help improve cholesterol and triglyceride levels.
Meat is a source of lean protein and is considered a staple on the ketogenic diet. Fresh meat and poultry contain no carbohydrates and are rich in B vitamins and several minerals, including potassium, selenium and zinc. While processed meats, like bacon and sausage, are allowed on keto, they aren't the best for your heart and may raise your risk of certain types of cancer if you eat too much. Choose chicken, fish and beef more often and limit processed meats.
Eggs are high in protein, B vitamins, minerals and antioxidants. Two eggs contain zero carbohydrates and 12 grams of protein. Eggs have been shown to trigger hormones that increase feelings of fullness and keep blood sugar levels stable, and they also contain antioxidants such as lutein and zeaxanthin, which help protect eye health.
Nuts and seeds are full of healthy polyunsaturated and monounsaturated fats, fiber and protein. They also are very low in net carbs. Olive oil and coconut oil are the two oils recommended on the keto diet. Olive oil is high in oleic acid and is associated with a lower risk of heart disease. Coconut oil is high in saturated fat but contains medium-chain triglycerides (MCTs), which can increase ketone production. MCTs may increase metabolic rate and promote the loss of weight and belly fat too. Measure portion sizes when consuming any type of healthy fat.
Carb counts for 1 oz. (28 g) of nuts and seeds (net carbohydrate equals total carbs minus fiber):
Berries are rich in antioxidants that reduce inflammation and protect against disease. They are low in carbs and high in fiber.
Carb counts for 1/2 cup of some berries:
Plain coffee and tea contain zero grams of carbohydrates, fat or protein, so they are A-OK on the keto diet. Studies show coffee lowers the risk of cardiovascular disease and type 2 diabetes. Tea is rich in antioxidants and has less caffeine than coffee; drinking tea may reduce the risk of heart attack and stroke, help with weight loss and boost your immune system.
Check the label on these, as the amount of carbs depends on the type and how much you consume. Cocoa has been called a "superfruit" because it is rich in antioxidants, and dark chocolate contains flavanols, which may reduce the risk of heart disease by lowering blood pressure and keeping arteries healthy.
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Don't get too discouraged. Dietitians Stone and Dority say that no foods are really off-limits on the keto diet. It's about total carbohydrate intake and how you choose to "spend" your carbs. Generally, you should stay under 20-40 grams of carbohydrates per day. "The exact amount needed to achieve ketosis can vary on the individual, though, with carb prescriptions ranging from 10 to 60 grams per day. This total is for net carbohydrates (total carbs minus fiber)," says Stone.
Dority adds, "Individuals who are really active can eat more carbs (maybe more at the 40-gram level) than someone who is sedentary."
Bottom line: It's not a one-size-fits-all prescription, and it's crucial to work with a dietitian to ensure you're getting essential nutrients while maintaining ketosis.
Cereal, crackers, rice, pasta, bread and beer are high in carbohydrates. Even whole-wheat pasta and the new bean-based pastas are high in carbs. Consider alternatives like spiralized vegetables or shirataki noodles, which are healthier low-carb options. Sugary breakfast cereals and healthy whole-grain cereals are high in carbohydrates too and should be avoided or minimized. "A slice of bread is 11 grams of carbs on average so technically you could have one slice a day maybe but that's spending all your carbs on pretty poor nutrition so I wouldn't recommend it when for the same carbs you could have A LOT of veggies," says Dority.
Beer can be enjoyed in moderation on a low-carb diet. Dry wine and spirits are better options but all alcohol should be very limited.
Starchy vegetables contain more digestible carbohydrates than fiber and should be limited on the ketogenic diet. These include corn, potatoes, sweet potatoes and beets. Limit high-sugar fruits too, which spike your blood sugar more quickly than berries and have more carbohydrates.
Carb counts for high-sugar fruits:
Carb counts for starchy vegetables:
Stick to plain yogurt to limit added sugars (aka carbohydrates). Greek yogurt is higher in protein and lower in carbohydrates compared to regular yogurt.
Fruit juice—natural or not—is high in fast-digesting carbs that spike your blood sugar. Stick to water.
Avoid sugar, honey, maple syrup and other forms of sugar, which are high in carbohydrates and low in nutrients.
Avoid chips, crackers and other processed, grain-based snack foods, which are high in carbohydrates and low in fiber.
Gluten-free does not equal carb-free. In fact, many gluten-free breads and muffins are as high in carbohydrates as traditional baked goods. They usually lack fiber too.
You can technically have any food on the keto diet if it falls within your daily carbohydrate goal, but these foods fall in the middle between high-carb and low-carb.
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Milk is an excellent source of calcium, potassium and several B vitamins. But, 1 cup has 12 grams of sugar (lactose). Choose almond, coconut or another low-carb milk instead.
Beans and legumes are high in fiber and protein and are part of a heart-healthy diet but are also high in carbohydrates. They may be included in small amounts on a ketogenic diet. However, it's often recommended to avoid them altogether.
There's promising research on the benefits of the ketogenic diet for many conditions, but some people can't keep it up for the long haul, plus the long-term effects are poorly understood. If you decide to go keto, work with a dietitian to help you create a plan.