Medically Reviewed by Kelly Kennedy, RD
If you’re looking to get a jump start on your health and fitness goals this year, you may be thinking about trying the ketogenic diet. Maybe you’ve heard the phrase before — it’s a huge diet buzzword — but aren’t sure what it means. Here’s a primer: The ketogenic diet is an eating plan that drives your body into ketosis, a state where the body uses fat as a primary fuel source (instead of carbohydrates), says Stacey Mattinson, RDN, who is based in Austin, Texas.
When you’re eating the foods that get you there (more on that in a minute), your body can enter a state of ketosis in one to three days, she adds. During the diet, the majority of calories you consume come from fat, with a little protein and very little carbohydrates. Ketosis also happens if you eat a very low-calorie diet — think doctor-supervised, only when medically recommended diets of 600 to 800 total calories.
Before you dive in, it's key to know the possible benefits and risks of keto.
There are three instances where there’s research to back up a ketogenic diet, including to help control type 2 diabetes, as part of epilepsy treatment, or for weight loss, says Mattinson. “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. They 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.
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’s 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 of 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 effective 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. (1) A meta-analysis noted that one reason for weight loss is likely that keto diets suppress hunger. (2)
One downside to a ketogenic diet for weight loss is the difficulty maintaining it. “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.
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.
If you’ve decided to move forward in trying the keto diet, you will want to stick to the parameters of the eating plan. Roughly 60 to 80 percent of your calories will come from fats. That means you’ll eat meats, fats, and oils, and a very limited amount of nonstarchy vegetables, she says. (This is different from a traditional low-carb diet, as even fewer carbs are allowed on the keto diet.)
The remaining calories in the keto diet come from protein — about 1 gram (g) per kilogram of body weight, so a 140-pound woman would need about 64 g of protein total. As for carbs: “Every body is different, but most people maintain ketosis with between 20 and 50 g of net carbs per day,” says Mattinson. Total carbohydrates minus fiber equals net carbs, she explains.
One thing to remember: “It’s easy to get ‘kicked out’ of ketosis,” says Mattinson. Meaning, if you eat something as small as a serving of blueberries, your body could revert to burning carbohydrates for fuel rather than fat.
One state is natural and generally harmless, whereas the other is a medical emergency. Here are the other key differences between the two.
Wondering what fits into a keto diet — and what doesn’t? “It’s so important to know what foods you’ll be eating before you start, and how to incorporate more fats into your diet,” says Kristen Mancinelli, RD, author of The Ketogenic Diet: A Scientifically Proven Approach to Fast, Healthy Weight Loss, who is based in New York City. We asked her for some guidelines.
Liberally: (That said, ketogenic diets aren’t high in protein, they focus on fat, so these should all be consumed in moderation.)
Occasionally: (Limit your consumption, which should be easy to do when avoiding packaged foods, which these are often found in.)
Occasionally: (These are still great choices, but you’ll also need to count these carbs.)
Liberally: Practice moderation with sweeteners.
Liberally: (All herbs and spices fit in a keto diet, but if you’re using large amounts, Mancinelli recommends counting the carbs.)
Occasionally: (These are still great choices, but contain some carbs.)
Optional: (These help you produce ketones more quickly, but Mancinelli says she has no opinion either way on recommending you take them or not.)
Following are some of the best foods to eat on the keto diet, along with their serving sizes and an explanation of why they’re good for people following this eating approach.
Per 1 tablespoon (tbsp) serving: 124 calories, 0g net carbs, 0g protein, 14g fat
Benefits: This is a good source of heart-healthy monounsaturated fatty acids.
Per 1 tbsp serving: 124 calories, 0g net carbs, 0g protein, 14g fat
Benefits: Research has shown that consumption of canola oil can reduce total and bad cholesterol. (3)
Per 1 tbsp serving: 116 calories, 0g net carbs, 0g protein, 14g fat
Benefits: While high in saturated fat, coconut oil may increase “good” HDL cholesterol levels.
Per 1 tbsp serving: 115 calories, 0g net carbs, 0g protein, 14g fat
Benefits: Derived from coconut, MCT stands for medium chain triglycerides. Limited research suggests MCT oil may aid in weight loss and help promote ketosis.
Per 1 tbsp serving: 100 calories, 0g net carbs, 0g protein, 11g fat
Benefits: Though the serving provides 11g of saturated fat, research has found that butter wasn’t a major factor in increasing risk of chronic conditions, like heart disease or diabetes. (4)
Per 1 slice serving: 113 calories, 0g net carbs, 7g protein, 9g fat
Benefits: Cheese is allowed as you please, but cheddar is a good example of its nutrition stats. One study found that cheese eaters had a 12 percent lower risk of type 2 diabetes. (5)
Per 1 tbsp serving: 52 calories, 0g net carbs, 0g protein, 5g fat
Benefits: This is an easy way to add calories and fat into a ketogenic diet.
Per 1 slice serving: 43 calories, 0g net carbs, 3g protein, 3g fat
Benefits: The green light on bacon may be one reason you’re up for sticking to the diet, as it can make eating occasions more palatable. Just watch the sodium content, as it can add up quickly.
Per 1 thigh serving: 318 calories, 0g net carbs, 32g protein, 20g fat
Benefits: Leave the skin on here for extra fat. One thigh is a good source of selenium, zinc, and B vitamins.
Per 1 egg serving: 77 calories, 1g net carbs, 6g protein, 5g fat
Benefits: Eggs contains the perfect duo of satiating protein and fat; they’re also high in the antioxidant mineral selenium.
Per 3-ounce (oz) serving (measured raw): 279 calories, 0g net carbs, 12g protein, 24g fat
Benefits: Ground beef (made with 70 percent lean meat and 30 percent fat) is a higher-fat choice — but that’s the point here. You’ll also get an excellent source of vitamin B12, which is necessary to keep energy levels up.
Per 3-oz serving: 224 calories, 0g net carbs, 22g protein, 14g fat
Benefits: You’ll get an impressive amount of muscle-building protein plus satiating fat in this option. It’s also rich in zinc, a mineral that promotes proper thyroid functioning.
Per 1 cup (raw) serving: 27 calories, 2g net carbs, 3g protein, 0g fat
Per ½ avocado serving: 160 calories, 2g net carbs, 2g protein, 15g fat
Benefits: The creamy fruits are packed with fiber, something that you may lack on the keto diet. They also are an excellent source of immune-revving vitamin C.
The ketogenic diet can result in fast weight loss, but it isn’t for everyone.
Per 1 cup (shredded) serving: 9 calories, 1g net carbs, 1g protein, 0g fat
Benefits: Chinese cabbage is a rich source of vitamins A and C, plus offers some calcium and energy-revving iron.
Per 1 cup (raw) serving: 25 calories, 2g net carbs, 2g protein, 0g fat
Benefits: Provides more than three-quarters of your vitamin C quota in a day; with 3 g of fiber, it's also a good source of the heart-healthy nutrient.
Per 1 cup (raw) serving: 16 calories, 1g net carbs, 1g protein, 0g fat
Benefits: Celery is one of the most hydrating veggies out there. These crunchy spears also contain vitamins A and K, and folate.
Per ½ cup (slices) serving: 8 calories, 2g net carbs, 0g protein, 0g fat
Benefits: Cukes are high in water, making them a hydrating choice. They’re also a surprisingly good source of vitamin K, a vitamin important for proper blood clotting and bone formation.
Per 1 cup (sliced) serving: 18 calories, 2g net carbs, 1g protein, 0g fat
Benefits: Along with more than a day’s requirements for vitamin C, they’re also a good source of vitamin B6, which plays a role in more than 100 enzyme reactions in the body.
Per 1 cup (shredded) serving: 5 calories, 1g net carbs, 0g protein, 0g fat
Benefits: Leafy greens can add bulk to your meals for very few calories, as well as skin-strengthening vitamin A and vitamin C.
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Per 1 cup (raw) serving: 15 calories, 1g net carbs, 2g protein, 0g fat
Benefits: Mushrooms are known for their potential immune-boosting properties, as one study suggested. (6) They’re also an excellent source of B vitamins.
Per 1 cup (sliced, raw) serving: 18 calories, 3g net carbs, 1g protein, 0g fat
Benefits: This is a great way to sneak in additional fiber, and the veggie also offers a good source of manganese, a mineral that helps form bone and aids in blood sugar control.
Breakfast: Scrambled eggs in butter on a bed of lettuce topped with avocado
Snack: Sunflower seeds
Lunch: Spinach salad with grilled salmon
Snack: Celery and pepper strips dipped in guacamole
Dinner: Pork chop with cauliflower mash and red cabbage slaw
Breakfast: Bulletproof coffee (made with butter and coconut oil), hard-boiled eggs
Snack: Macadamia nuts
Lunch: Tuna salad stuffed in tomatoes
Snack: Roast beef and sliced cheese roll-ups
Dinner: Meatballs on zucchini noodles, topped with cream sauce
Breakfast: Cheese and veggie omelet topped with salsa
Snack: Plain, full-fat Greek yogurt topped with crushed pecans
Lunch: Sashimi takeout with miso soup
Snack: Smoothie made with almond milk, greens, almond butter, and protein powder
Dinner: Roasted chicken with asparagus and sautéed mushrooms
Breakfast: Smoothie made with almond milk, greens, almond butter, and protein powder
Snack: Two hard-boiled eggs
Lunch: Chicken tenders made with almond flour on a bed of greens with cucumbers and goat cheese
Snack: Sliced cheese and bell pepper slices
Dinner: Grilled shrimp topped with a lemon butter sauce with a side of asparagus
Breakfast: Fried eggs with bacon and a side of greens
Snack: A handful of walnuts with a quarter cup of berries
Lunch: Grass-fed burger in a lettuce “bun” topped with avocado and a side salad
Snack: Celery sticks dipped in almond butter
Dinner: Baked tofu with cauliflower rice, broccoli, and peppers, topped with a homemade peanut sauce
Breakfast: Baked eggs in avocado cups
Snack: Kale chips
Lunch: Poached salmon avocado rolls wrapped in seaweed (rice-free)
Snack: Meat-based bar (turkey or pork)
Dinner: Grilled beef kabobs with peppers and sautéed broccolini
Breakfast: Eggs scrambled with veggies, topped with salsa
Snack: Dried seaweed strips and cheese
Lunch: Sardine salad made with mayo in half an avocado
Snack: Turkey jerky (look for no added sugars)
Dinner: Broiled trout with butter, sautéed bok choy