Low-Carb Diets: What They Are and How They Compare

The short version

• Low-carb generally means under about 130 grams of carbs a day. Keto is a much stricter version.
• It often produces faster loss at first, partly from water, but long-term results look similar to other diets.
• It can improve blood sugar and triglycerides, so it's worth discussing if you have diabetes.
• Quality matters. Non-starchy vegetables, fish, nuts and olive oil beat bacon and processed meats.

In a sentence

Cut sugar and starches, and eat more protein, fat and vegetables.

How restrictive

Counting needed?

Carbs, usually

Quality of evidence

Moderate

Typical cost

Moderate to high

Main drawback

Can run low on fiber, and LDL cholesterol can rise in some people

See how this compares with every other diet →

What counts as low-carb

There's no official definition, but these ranges are common:

Well-known versions include Atkins, South Beach and many others.

What you eat

• Eat freely: Non-starchy vegetables, fish, poultry, eggs, tofu
• Moderate amounts: Nuts, seeds, cheese, olive oil, avocado, berries, plain yogurt
• Limit: Beans, fruit, whole grains, starchy vegetables
• Mostly avoid: Sugary drinks, sweets, white bread, chips, pastries

What the evidence says

Weight. Low-carb often leads to faster early loss, partly because you lose water along with stored carbs. By a year, differences mostly disappear. In DIETFITS, healthy low-carb and healthy low-fat diets came within about 2 pounds of each other. A review of 19 trials found little or no difference between low-carb and balanced diets when calories were similar.

Why it works when it works. Removing refined carbs takes out many of the foods that are easiest to overeat, and the extra protein keeps you full. So people often eat less without trying.

Blood sugar and triglycerides. Eating fewer carbs tends to lower blood sugar and triglycerides, often within weeks. This makes it attractive if you have prediabetes or type 2 diabetes.

Cholesterol. LDL ("bad") cholesterol can rise, especially if you add a lot of saturated fat. It varies from person to person, so have it rechecked after a few months.

How to do it well

• Build meals from vegetables and lean protein, then add healthy fats. The goal isn't unlimited bacon.
• Pick fish, olive oil, nuts and avocado as your main fats.
• Watch your fiber, since it's easy to fall short. Lean on vegetables, berries, nuts and chia or flax seeds.
• Drink plenty of water, and expect the first week to feel a bit rough.

Pros and cons

Good: Simple rules, good for appetite, good for blood sugar.

Harder: Restaurant and social meals can be tricky, it can cost more, and many people feel restricted over time. Constipation and "low-carb fatigue" are common at first.

Sources

1. Gardner et al., JAMA (2018): Low-fat vs low-carb diet (DIETFITS)
2. Naude et al., PLoS One (2014): Low-carbohydrate vs balanced diets
3. Harvard T.H. Chan School of Public Health: Diet Review: Ketogenic Diet

This guide is general information, not medical advice. Please check with a clinician before making big changes, especially if you have a health condition, take medication, or are pregnant. Read the full disclaimer.