Learn the similarities and differences between these two diets and find out if either one is worth following for weight loss or general health.

Everyone loves to hate carbs. They've gotten a bad reputation recently and are blamed for everything from causing diabetes to poor energy levels (not all carbs are bad for you FYI). But what is a low-carb diet anyways? And isn't keto low-carb too? Read on to learn the differences between a low-carb diet and a ketogenic diet, plus find out which one is better for weight loss and overall health.

What is a low-carb diet?

There is no standard definition for a low-carb diet. It is simply a diet that is lower in carbohydrates than what is recommended or than what most people consume. The Dietary Guidelines recommend that 45-65 percent of calories come from carbohydrates. So any diet with carb intake less than 45 percent of total calories is considered a low-carb diet. Studying the effects of low-carb diets on health outcomes is difficult since there is no standard definition for low-carb. See our low-carb meal plans created by a registered dietitian.

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What is the keto diet?

The ketogenic (keto) diet falls under the definition of a very low-carbohydrate diet, which is a diet with less than 50 grams of carbohydrates per day. Five percent or less of calorie intake is from carbs on the keto diet, which is about 20-50 grams per day, depending on your total energy intake.

The keto diet was introduced by physicians in the 1920s for treating epilepsy, but has since become a popular weight loss diet. Since it's very low-carb, people lose weight rapidly, hence why it is enticing to try. The keto diet may also help control blood sugars and improve some neurological disorders (learn more about if the ketogenic diet is right for diabetes). But the effects of being on the diet long-term are unknown.

What's the nutrient breakdown?

There are three macronutrients: carbohydrates, protein, and fat. When you cut back on carbs, you replace those carbohydrate calories with another macronutrient—usually fat. This leads to a low-carb, moderate protein, high-fat diet.

For example, if someone follows a low-carb diet with 30 percent of calories from carbs and the recommended 10-20 percent from protein, it means that about 50-60 percent of their calories will come from fat.

The breakdown of macros on the keto diet is about 80 percent calories from fat, 15-20 percent from protein and less than 5 percent from carbohydrates. Contrast that with the Dietary Guidelines recommendation of 25-35 percent calories from fat, 10-30 percent from protein and 45-65 percent from carbohydrates.

How does each diet work?

The body prefers to use glucose—a carbohydrate—as its energy source. When carbohydrate intake is very low (<50 grams) and glucose isn't available for energy, the body makes glucose from other sources. This is called gluconeogenesis.

When carb intake is even lower than this, like on the keto diet, and the body can't make enough glucose for its needs, the body enters a metabolic state called ketosis where it breaks down fat for energy into ketone bodies (learn more about ketosis and what happens in your body). Once you reach ketosis, most cells will use the ketones created by ketosis for energy until you start eating carbohydrates again.

Key similarities between low-carb and keto

Both diets are low in carbohydrates, but the keto diet is lower in carbs (<5 percent calories from carbs) and higher in fat.

Neither diet technically restricts entire food groups, unless the food pushes you over the carb limit for the day. Grains, legumes, dairy, fruits, vegetables, processed foods, sugary foods, and some alcohol are restricted for this reason (here's a complete list of foods you can and cannot eat on the ketogenic diet).

Which one is better for weight loss?

Both a low-carb diet and keto diet can help you lose weight. When you eat carbohydrates, the hormone insulin is released to take glucose to your cells for energy. Extra glucose is stored as glycogen but if there's glucose leftover after that, insulin stores the rest as fat. When you cut carbs, not as much insulin is released so the body can be in fat burning mode instead of fat storing mode. You will also likely end up cutting down your calorie intake, since the foods you can eat are limited.

But, a lot of things can help you lose weight quickly. The question is: Which pattern of eating can you keep up with for the long term? Although you may lose weight on a low-carb or keto diet, if you can't eat that way forever, you won't keep the weight off forever.

Research backs this too. Countless studies have tried to figure out if low-carb or low-fat is better for weight loss. Most reach the same conclusion: Low-carb diets can lead to faster weight loss in the short-term, but at one to two years follow-up, the weight loss outcomes are the same for low-carb and low-fat dieters.

A 2017 study in overweight adults with type 2 diabetes found that after one year, those that followed a ketogenic diet lost more weight and had lower A1Cs than those following a low-fat diet.

Few to no studies have compared the effects of low-carb diets to ketogenic diets on weight loss or other health outcomes.

Which is better for overall health?

The ketogenic diet is proven effective in children with epilepsy, and emerging research shows it may provide benefits for a number of neurological disorders. Research shows keto might also help those with type 2 diabetes better control blood glucose levels and potentially reduce their A1C. More research is needed though. The effects of following keto long-term are unknown. It is difficult to study since most people have trouble complying to such low carbohydrate intake for years.

For non-keto, low-carb diets, a 2015 and 2016 study concluded that even though low-carb diets are safe in the short-term and effective, there were no differences on blood sugar response compared to a diet with more carbs for people with type 2 diabetes and that total calorie intake is still the best predictor of weight loss. Learn more about how to eat healthy when you have diabetes.

Downsides of eating low-carb or keto

You may have heard of the "keto flu," a nasty side effect of the ketogenic diet that causes dizziness, nausea, and fatigue due to losing fluid and sodium quickly after cutting carbs.

Another downside is the difficulty of following the keto diet. Many people eating keto might not actually be in a state of ketosis. It's recommended to follow keto under the supervision of a doctor or dietitian.

Both a low-carb diet and keto diet cut carbs, which means cutting fiber. Fiber suppresses appetite and slows digestion leading to weight loss and maintenance. Fiber also lowers risk for cardiovascular disease and helps stabilize blood sugars (try these 10 foods with more fiber than an apple).

Fiber is food for the good bacteria in your gut. These bugs feed off of non-starchy vegetables, fruit, whole grains, beans, and legumes - all foods that are limited on low-carb diets. A healthy microbiome is linked to improved heart health, brain health, digestion, and immunity.

It is also well documented that eating whole grains is associated with a lower risk of heart disease and type 2 diabetes.

Eating a high percentage of calories from fat could also raise LDL ("bad") cholesterol levels and triglycerides. If eating low-carb, be sure to choose healthy fats like salmon, albacore tuna, olive oil, avocado, nuts and seeds.

There are less restrictive diets such as the Mediterranean diet that are associated with a healthy weight, reduced risk for heart disease and diabetes, and living longer. The Mediterranean diet is also a whole-body, holistic approach that includes daily movement, eating with others, and being social. This eating pattern is more sustainable for people to keep up with for their entire lives.

Things to consider before deciding on low-carb vs. keto

  • Before deciding to do any diet, ask yourself why you are going on the diet. Is it for weight loss or for something else?
  • Talk to your health care providers, including your physician and a dietitian, to determine which diet is best for you based on your goals.
  • Remember this: you'll only continue seeing results as long as you can keep up with the diet. Is the diet you're choosing compatible with your lifestyle? Do you eat out a lot or travel for work frequently? It's not impossible to eat low-carb or keto on the road, but (as with most diets) preparation and planning are key—as is working with a professional who can help you.

Bottom Line

There's no standard definition for a low-carb diet, but it generally refers to eating less than 45 percent of calories from carbs. The ketogenic diet is a high-fat, moderate protein, very low-carb diet with less than 5 percent of calories coming from carbohydrates. Both diets can help you lose weight, but studies show they don't work any better than low-fat diets for losing weight long-term. You may find it easier to follow a low-fat diet or a healthy eating pattern like the Mediterranean diet than to drastically cut carbs for the rest of your life.