Keto Diet for Beginners: Benefits, Risks and a Food List

A keto (ketogenic) diet cuts carbohydrates to roughly 20 to 50 g a day so that your body switches to burning fat and producing ketones for fuel. It can lead to fast early weight loss, but after a year, trials show results only slightly better than, or similar to, a conventional low-fat diet. It is also restrictive and not safe for everyone, so it is worth understanding before you start.

This keto diet for beginners guide covers how it works, what to eat, the realistic benefits, the side effects and who should avoid it.

How keto works

Your body normally runs mostly on glucose from carbohydrates. When you eat very few carbs, it first uses glucose stored in the liver and some from muscle. According to Harvard’s diet review, after about 3 to 4 days of very low carb intake, insulin levels fall and the body shifts to fat as its main fuel. The liver turns fat into ketone bodies, which the brain and other tissues can use. That state is called ketosis.

Nutritional ketosis is not the same as ketoacidosis, a dangerous build-up of acid in the blood that mainly affects people with type 1 diabetes. Rare cases of ketoacidosis have been reported in people without diabetes on prolonged very low-carb diets, which is one reason keto is not a casual experiment.

Keto macros: what a day looks like

There is no single standard keto diet. Harvard describes typical versions as:

• Carbohydrate: under 50 g a day, sometimes as low as 20 g (5 to 10% of calories)
• Fat: 70 to 80% of calories
• Protein: moderate, 10 to 20% of calories

For perspective, Harvard notes that 50 g of carbohydrate is less than you would get from one medium plain bagel.

Worked example for 1,800 kcal a day

Here is how that might look for someone eating 1,800 kcal who weighs 70 kg:

• Carbohydrate: 20 to 50 g × 4 kcal = 80 to 200 kcal, or about 4 to 11% of calories
• Protein: 70 kg × 1.4 g/kg = 98 g × 4 kcal = 392 kcal, about 22% of calories
• Fat: 1,800 − 200 − 392 = 1,208 kcal ÷ 9 ≈ 134 g, about 67% of calories

This version uses 1.4 g of protein per kg, a common everyday target, which lands slightly above the typical keto range. Classic keto keeps protein moderate because the body can turn some protein into glucose, which can interfere with ketosis. If you are unsure about protein, see our guide to how much protein per day.

Keto food list

Based on Harvard’s summary of what most keto plans allow and restrict:

Usually allowed	Limited or avoided
Olive oil, avocado, nuts (walnuts, almonds, macadamias), seeds	Bread, pasta, rice, cereals, all grains and flour products
Fish, especially oily fish, eggs, poultry, meat, tofu	Potatoes, corn and other starchy vegetables
Leafy greens, broccoli, cauliflower, courgette, peppers, mushrooms, asparagus	Beans, lentils, chickpeas and peanuts
Hard cheese and butter	Most fruit and all fruit juice
Berries in small portions	Sugar, honey, sweets and sugary drinks
Coffee and tea without sugar, herbs, spices, mustard, vinegar	Beer, sweet wine, cocktails

Two points worth knowing:

• Choose your fats carefully. Many keto plans allow lots of butter, lard, bacon and processed meat. That high saturated fat intake goes against heart-health guidelines and may raise LDL cholesterol. StatPearls notes that experts recommend prioritizing unsaturated fats such as olive oil, nuts and fatty fish.
• “Net carbs” are not a regulated term. Harvard explains that net carbs (total carbs minus fiber and sugar alcohols) were popularized by food marketing, and the effect of sugar alcohols on blood sugar varies. Read the full label; our guide on how to read nutrition labels helps.

What keto can and cannot do

Weight loss: real, but not magic

Keto often produces a big drop on the scale in the first week or two. StatPearls attributes much of that early loss to water, because the diet has a diuretic effect. Fat loss follows at a slower pace.

Over the longer term, a 2013 meta-analysis of 13 randomized trials with at least 12 months of follow-up found that very low-carb ketogenic diets led to about 0.9 kg more weight loss than low-fat diets. Keto groups also had lower triglycerides and higher HDL cholesterol, but higher LDL cholesterol. Harvard’s review concludes that after one year, keto’s effects are not significantly different from conventional weight-loss diets.

Does keto automatically reduce appetite?

Many people say keto makes them less hungry, and short studies in Harvard’s review found people reported less hunger than before they started. But in a tightly controlled 2021 NIH study, 20 adults who could eat as much as they wanted ate about 689 kcal a day more on an animal-based keto diet than on a plant-based, low-fat diet. Appetite effects differ between people, and calories still count.

For a broader look at how low-carb eating compares with low-fat eating, see low carb vs low fat.

Long-term safety is still unclear

Most keto studies are short, often 12 weeks or less. A 2021 review in Frontiers in Nutrition concluded that, given often temporary improvements, effects on diet quality and limited long-term safety data, for most people the risks of keto may outweigh the benefits. Keto remains an established medical therapy for some forms of epilepsy, under specialist supervision.

Side effects of keto

Short-term (“keto flu”): StatPearls lists nausea, constipation, diarrhea, headache, fatigue, dizziness and bad breath, usually in the first days to weeks. Harvard adds hunger, low mood, irritability and brain fog. Gastrointestinal complaints affect about half of people starting the diet. Drinking enough fluids and getting enough electrolytes usually helps.

Longer-term concerns reported in the literature include:

• Higher LDL cholesterol in some people
• Kidney stones
• Reduced bone density
• Raised uric acid, a risk factor for gout
• Low intake of fiber, B vitamins, iron, magnesium and zinc because whole grains, beans and most fruit are cut out

To reduce the fiber gap, load up on non-starchy vegetables, nuts and seeds. Our guide to how much fiber per day explains how much you need.

Who should not try keto

StatPearls and Harvard identify several groups for whom keto is risky or not recommended:

• People taking SGLT2 inhibitor medicines for diabetes: the combination can cause a dangerous form of ketoacidosis even when blood sugar looks normal.
• People on insulin or sulfonylureas: a sudden drop in carbs can cause low blood sugar, and doses usually need medical adjustment.
• Pregnancy and breastfeeding: not recommended, as safety has not been shown.
• A history of eating disorders: rigid food rules can trigger relapse.
• Pancreatitis, liver failure, and rare disorders of fat metabolism, including carnitine deficiencies, porphyria and pyruvate kinase deficiency.
• Kidney disease: high protein and ketosis may add to the kidneys’ workload.
• Children and teenagers: keto has been linked with slower growth in children treated for epilepsy, so it belongs only under a medical team.

If you have any ongoing health condition or take regular medication, see your doctor first. Harvard recommends that anyone starting keto consult a doctor and a dietitian to monitor changes and avoid nutritional gaps.

How to start keto more safely

If you are a healthy adult and still want to try it:

1. Get a baseline blood test for cholesterol if you can, and repeat it after a few months.
2. Build meals on vegetables, fish, eggs, olive oil, nuts and seeds, not bacon and butter.
3. Drink plenty of fluids and pay attention to electrolytes such as sodium, potassium and magnesium, especially if you feel “keto flu.”
4. Track your carbs honestly for the first weeks. Hidden carbs in sauces, dressings and “keto” snacks add up fast. Scanning barcodes of packaged foods, or photographing meals in PixNutri and checking the estimated carbs, makes this easier. PixNutri Pro also offers keto AI meal plans. Treat any estimate as a starting point and adjust it.
5. Keep total calories in mind. Keto does not cancel out a calorie surplus.
6. Plan your exit. Decide how you will move to a more flexible, lower-carb or Mediterranean-style pattern once you reach your goal.

FAQ

How many carbs can I eat on keto?

Most keto plans limit carbohydrates to under 50 g a day, and some to 20 g. The exact amount that keeps you in ketosis varies from person to person.

How long does it take to get into ketosis?

Harvard’s review describes it as usually taking about 3 to 4 days of very low carbohydrate intake, but it varies with your body and activity.

Is keto better than other diets for weight loss?

Only slightly, if at all. A meta-analysis found about 0.9 kg more weight loss than low-fat diets after a year or more, and Harvard concludes the long-term difference is not significant.

Is keto bad for your heart?

It depends on what you eat. Keto high in saturated fat can raise LDL cholesterol. A version based on olive oil, nuts and fish is a better choice, and it is wise to check your cholesterol.

Can I do keto if I have type 2 diabetes?

Only with your doctor’s supervision. Medicines such as insulin, sulfonylureas and SGLT2 inhibitors can cause dangerous reactions with a very low-carb diet.