Ketogenic Diet | What is Keto and the Best Keto Diet Foods?

Chances are you’ve heard of the ketogenic diet — a low-carb approach to weight loss that’s backed by more scientific research than most fad diets that come and go. This guide walks through everything worth knowing about the ketogenic diet, including a few details that often get left out.

What Is a Ketogenic Diet?

Often shortened to “keto,” the ketogenic diet is built around two simple principles: low carbs, high fat. In that sense, it shares some DNA with the well-known Atkins diet.

In practice, you cut carbs way down and lean into fat instead, which can raise your metabolic rate through a process called ketosis. Tracking your food intake matters quite a bit when starting out, since you’ll want to keep tabs on your carb, protein, and fat ratios.

The eventual payoff is that your body starts running more efficiently on fat for fuel. That not only supports weight loss — it also converts liver fat into ketones your body can use for energy.

What Are Ketones?

Ketones function as an energy source. When glucose runs low, the body turns to ketones as fuel instead, and the liver produces them as it breaks down fat. This process also gives your brain an extra energy boost, which many people report as sharper thinking.

Types of Ketogenic Diets

There’s more than one way to follow a ketogenic diet. The most common, the Standard Ketogenic Diet (SKD), calls for moderate protein and fat intake while keeping carbs extremely low — typically around 5% of total calories, with the rest split roughly 75% fat and 20% protein.

The Cyclical Ketogenic Diet takes a different approach, building in “refeed” days where carb intake goes up temporarily — often five strict keto days followed by two higher-carb days. Some research suggests these refeeds can actually boost metabolic rate.

There’s also a High-Protein Ketogenic Diet, similar to the standard version but with more protein — roughly 35% protein, 60% fat, and 5% carbs. Worth noting: the standard and high-protein versions are the two variations with the most research behind them.

How the Ketogenic Diet Works

Research suggests the ketogenic diet can outperform a standard low-fat diet for weight loss. Part of the appeal is that it’s genuinely filling, which makes it easier to stick with without constant hunger. In follow-up studies, participants on keto lost more than double the weight of those following a low-fat diet — likely thanks in part to the diet’s higher protein content, which plays an important role in satiety and overall health.

Ketogenic Diet Foods to Avoid

The core idea is limiting carbs, and tracking your intake is the most reliable way to stay on target. Foods worth skipping include:

Sweets

Anything high in sugar — candy, soda, cake, ice cream.

Fruit

Most fruit is high in natural sugar, though berries in moderation are generally fine.

Starches

White flour and wheat products like pasta, bread, and cereal are carb-heavy and best avoided.

Root Vegetables

Potatoes, carrots, and similar vegetables carry more carbs than people expect.

“Diet” Products

Many packaged diet foods are heavily processed and loaded with carbs despite their marketing.

What to Eat on the Ketogenic Diet

The good news is there’s a wide variety of satisfying foods on keto, including plenty of dishes you’d otherwise avoid on a low-fat plan.

Meat, Cheese, and Eggs

Red meat, chicken, fatty fish like salmon and trout, turkey, and eggs are all keto staples. Unprocessed cheeses — goat, blue, cheddar — work well in moderation.

Nuts, Avocados, and Low-Carb Vegetables

Walnuts and almonds help curb hunger, avocados bring healthy fat and flavor, and leafy greens, tomatoes, peppers, and onions round out the plate.

Healthy Oils and Condiments

Extra virgin olive oil, avocado oil, and coconut oil are all solid choices, and most herbs and spices without added sugar are fair game.

Keto Diet Side Effects

The ketogenic diet is safe for most people, though some experience side effects as the body adapts — commonly called “keto flu.” This adjustment period typically lasts only a few days and can include hunger, low energy, trouble concentrating, nausea, and mild sleeplessness. Easing into the diet gradually rather than cutting carbs all at once, and staying on top of your water and mineral intake, can help minimize these symptoms.

Frequently Asked Questions About the Ketogenic Diet

Does the keto diet cause muscle loss?

It’s unlikely, since the diet emphasizes high protein and healthy fat intake, both of which help protect muscle mass. If building muscle is your main goal, though, a moderate-carb diet may serve you better.

Are carbs off-limits forever?

No — the strict carb restriction mainly applies during the first two to three months. After that, most people can reintroduce carbs in moderation.

Why does keto sometimes cause bad breath?

Ketosis itself can cause a distinct breath odor, especially early on. Chewing gum or drinking flavored water can help manage it.

The Bottom Line on the Ketogenic Diet

The ketogenic diet tends to work best for people carrying excess body fat or looking to improve metabolic health. If building muscle mass is the priority, a moderate-carb approach may be a better fit. For everyone else, keto has real research behind it — the results come from sticking with it consistently, day after day.

Explore more Healthy Diet reviews and guides on our site.

For general guidance on healthy weight management, see the resources available from Mayo Clinic.