Physical

The Keto Diet: How It Works, Who It Suits and Tips for Doing It Safely

An honest guide to the ketogenic diet: what ketosis is, what the research says about weight loss, common side effects, who should avoid keto and practical tips.

Updated October 10, 2026 · 3 min read

Keto has fans who swear by it and critics who think it's a fad. The truth sits somewhere in the middle, and knowing how it works will help you decide whether it's for you.

What the keto diet actually is

The ketogenic diet is very low in carbohydrates, moderate in protein and high in fat. Most versions keep carbs to roughly 20 to 50 grams a day. For comparison, one medium banana has about 27 grams.

When carbs drop that low, your body runs short on glucose, its usual fuel. Your liver starts turning fat into molecules called ketones, which your brain and muscles can use for energy. That state is called ketosis.

Keto wasn't invented for weight loss, by the way. Doctors have used it since the 1920s to help control seizures in some people with epilepsy, and it's still used for that today under medical supervision.

Does keto work for weight loss?

People often lose weight quickly in the first week or two. A good chunk of that early drop is water, because carbs are stored in your body along with water.

Over the longer term, research generally finds that keto can work about as well as other diets that cut calories, but not dramatically better. The best diet for weight loss tends to be the one you can actually stick with. Some people find keto's rules make that easier because they feel less hungry. Others find cutting out bread, fruit and pasta miserable.

Common side effects

  • "Keto flu": headache, tiredness, brain fog and irritability in the first week or so as your body adjusts. Drinking plenty of fluids usually helps.
  • Constipation: low-carb eating can mean low fiber. Lean on non-starchy vegetables.
  • Cholesterol changes: some people see their LDL ("bad") cholesterol rise on keto, especially when the fat comes mostly from butter, cheese and fatty meat.
  • Hard to keep up socially: shared meals, holidays and eating out get tricky.

Who should avoid keto or check with a doctor first

Talk to your doctor before starting keto if you:

  • have type 1 or type 2 diabetes, especially if you take insulin or other medicines that lower blood sugar
  • have kidney disease, liver disease or a history of pancreatitis
  • are pregnant or breastfeeding
  • have had an eating disorder
  • take medicine for blood pressure

Tips if you decide to try it

  1. Build your plate around vegetables. Leafy greens, broccoli, cauliflower, zucchini, peppers and mushrooms are low in carbs and high in fiber.
  2. Choose mostly unsaturated fats. Olive oil, avocado, nuts, seeds and oily fish like salmon are better bets for your heart than piling on bacon and butter.
  3. Don't fear protein, but don't overdo it. Eggs, fish, chicken, tofu and Greek yogurt are all useful.
  4. Read labels. Sauces, dressings and "healthy" snacks often hide sugar.
  5. Drink water and get enough salt from food. Early on, your body flushes out water and sodium.
  6. Plan your exit. Decide ahead of time how you'll reintroduce carbs, so you don't swing straight back to old habits.
  7. Get a checkup. Ask your doctor to check your cholesterol a few months in.

Want a done-for-you starting point? See our 14-day keto meal plan.

Keep reading