As we’ve mentioned, many people equate “low-carb” with “keto.” In reality, many variations of the low-carbohydrate diet are relatively popular in America.

There’s one thing it helps to know first: the USDA’s Dietary Guidelines for Americans suggest that people get 45-65% of their daily calories from carbohydrates. That means the normal U.S. diet would contain between 225 and 325 grams of net carbs per day. (A food’s net carbs is calculated by deducting grams of fiber – which can’t be digested – from total grams of carbs.)

• Standard Low-Carb Diet: These dieters simply reduce the amount of grains and sugar that they eat, without any firm rules or carb counting. They avoid foods like potatoes, soft drinks, fast food and junk food, and try to eat more protein, fruits and vegetables. Even an eating plan that cuts carbs to 100 grams of carbs (often abbreviated to “100 carbs”) is considered low-carb.
• Low-Carb, High Fat Diet: The so-called LCHF diet is similar to the standard low-carb one, but with a greater focus on unprocessed whole foods. Carb consumption can be anywhere between 20-100 daily carbohydrates, depending on whether the diet is considered strict, medium or liberal.
• Atkins Diet: Dieters eat a maximum of 20 grams of carbs for two weeks, and then slowly add carbs back into their diet in stages as they lose weight. A variation called Eco-Atkins is a combination of Atkins and vegan eating.
• Paleo Diet: This is more of a philosophical approach to eating than a strict diet plan. Dieters eat the same foods people ate in the Paleolithic Era: unprocessed proteins, fruits, vegetables, nuts and seeds. No processed or packaged foods are allowed, meaning grains and sugars are excluded. That automatically makes the diet low in carbohydrates, so no carb counting is needed.
• Low-Carb Mediterranean Diet: This version of the popular diet emphasizes fish, poultry, healthy fats like olive oil, veggies and fruit, seeds and nuts, and red wine – but leaves out the whole grains encouraged on the regular Mediterranean diet.
• Ketogenic Diet: This high-fat (and sometimes high-protein) diet differs from most other low-carb diet plans because carbs are very strictly limited for the full length of the keto diet. Some versions allow up to 50 daily grams of carbs, but most people following keto limit carbs to 20 or 25 per day.
• Zero-Carb Diet: Some go all the way and eliminate virtually all carbs from their diet, but dietitians and health care professionals warn that zero-carb may not be safe.

You’ve probably noticed that strict low-fat diets like keto set a very low bar for carbohydrate intake, at 20-25 grams. There’s a biological reason for that.

On a normal diet, the carbs we eat are turned into glucose (blood sugar). Glucose is the primary energy source for the body and brain. However, unused glucose is stored in the body, much of it as a type of body fat called triglycerides. That’s why eating too much sugar and starch can lead to excess weight or obesity.

On keto and other very low-carb diets, the body doesn’t get enough carbs to produce the glucose it needs for energy. When that happens, the body enters a metabolic state called ketosis – and in ketosis, it burns stored fat to create a different type of fuel.

In ketosis, the body produces molecular bodies called ketones to be used as its energy source. As long as the body doesn’t get enough carbs to make glucose, it continues to burn stored fat to make more ketones. And fat-burning = weight loss.

In most cases, the body “falls out of ketosis” as soon as it gets more than 20-25 carbs. That explains why the carb limits on keto and similar diets are so strict; just a single cheat day can stop the weight loss. But strict adherence to very low-carb eating plans can produce impressive results.

(One warning: when people start keto or other diets that will put them into ketosis, they commonly suffer side effects known as the “keto flu.” The headache, constipation, insomnia and fatigue usually only last a few days, though.)

Very low-carb diets are considered to be the best weight-loss diets for fast results. And clinical trials have shown that low-carb diets are more effective than the low-calorie or low-fat diets that were popular for years.

However, many medical professionals say diets like keto should only be a short-term approach, followed by sensible eating (including low-carb foods) and regular physical activity.

Yes, and they can provide a number of health benefits as well.

Keto and other very low-carb eating plans often produce initial water weight loss of 5-10 pounds, and an average of 1-2 pounds of fat loss per week after that – as long as the dieter remains in ketosis. But you don’t have to go draconian to lose weight.

Limiting carbs to 50-100 grams per day can produce slow but steady weight loss. One reason is that low-carb diets reduce insulin levels in the body, and that’s been associated with weight loss. (It can also reduce the risk of developing type-2 diabetes.)

Another is that people eat more protein on a low-carb diet, and protein consumption has been shown to decrease appetite and increase metabolism (which promotes fat-burning). And the fat that’s burned is most likely to be belly fat, the least-healthy type of fat to carry long-term.

One more reason: eliminating the junk food that’s a major source of carbs in most people’s diets reduces the brain’s craving for “rewarding” sugar and junk food.

The additional health and wellness benefits of low-carb dieting are also notable. They include:

• Increased HDL cholesterol levels (“good cholesterol”)
• Lowered LDL cholesterol levels (“bad cholesterol”)
• A dramatically lower risk of metabolic syndrome, which can increase the risk of diabetes and cardiovascular disease
• Lower blood sugar levels and insulin resistance
• A drop in high blood pressure
• A proven treatment for some forms of epilepsy; may be helpful against neurological diseases like Alzheimer’s and Parkinson’s

Low-carb diets, particularly very low-carb alternatives like keto, could cause issues for some patients. Diabetics, people who have kidney problems, those with eating disorders and those who are pregnant are often advised not to try low-carb eating. The best advice: always consult with medical professionals before beginning a diet of any kind.