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What Is a Low-Carb Diet? Does That Mean It’s Keto?
This article has been written by experts and fact-checked by experts, including licensed nutritionists, dietitians or medical professionals. The information in the article is based on scientific studies and research.
It is designed to be honest, unbiased and objective, and opinions from both sides of an argument are presented wherever there is disagreement.
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Early in grade school, you probably learned that “all humans are animals – but not all animals are human.”
That’s the easiest way to explain low-carb dieting and its relationship to the incredibly-popular keto diet: keto is a low-carb diet – but not all low-carb diets are keto.
All low-carb diets require you to make major changes in the way you eat. You have to reduce the number of carbohydrates you normally eat each day; you replace them in your diet with more of the other two macronutrient food groups, fats and proteins.
What makes that different from the ketogenic diet? The details. Generally speaking, on most low-carb diets you’re allowed to eat more carbs and less fat than when you’re on keto.
We’ll get more specific shortly, after we explain those details and the reasoning behind low-fat diets. We’ll also explore the big question: do they work?
Low-Carb Diets: What You Can and Can’t Eat
Most of us have heard since we were little that we should eat less junk, and more fruits and vegetables. We’ve also heard we should stay away from fats and fatty meat. Low-fat foods, whole grains and lean proteins are supposedly the keys to good health – and weight loss.
Low-carbohydrate diets turn much of that common wisdom on its head.
Junk food and calorie-laden desserts are still off-limits, as you’d probably guess. But so are some vegetables and fruits. Lean proteins are OK, but fatty proteins are better. “Low-fat” and “diet” foods are bad, and whole grains are bad. But healthy fat is good.
What’s going on here?
A Look at Carbs
Quite simply, a low-carb diet is just what it sounds like. You eliminate most high-carb foods, and key offenders in that regard are sugars and starches. That explains why junk food and sugary desserts are no-nos. And while whole grain bread and pasta are healthier than foods made with white flour, they’re still loaded with carbs.
“Low-fat” products often make up for the absence of fat with – yep – added sugar. There are all kinds of sugars in packaged and processed foods, too.
But what could be wrong with fruits and vegetables? Two words: hidden carbohydrates.
Many veggies and almost all fruits are loaded with carbs. Fruit certainly contributes vitamins and minerals, as well as fiber, to a diet. But it’s also loaded with fructose, which is nothing more than a form of sugar. Vegetables are another great source of dietary nutrients, but many of them (particularly the ones that grow below ground, as well as legumes like beans) contain lots of starch.
At least some fruits and veggies have to go when you’re limiting your carb intake; the specifics depend on which type of low-carb eating plan you’ve chosen. Non-starchy vegetables are encouraged, and only berries and a few select fruits are allowed as occasional treats.
There are other foods with hidden carbs that can be a problem for low-carb dieters, and many of them are dairy products. We’ve all heard of lactose, because most of us have a family or friend who’s lactose-intolerant. But what is lactose? It’s “milk sugar,” another type of sugar that’s nothing but carbs.
So milk and some other dairy products are problematic when you’re on a low-carb meal plan. Heavy cream, on the other hand, is one of the standards of low-carb dieting.
How is that possible?
A Look at Fat
Three macronutrients make up our diet: carbs, fat and protein. So when you eliminate almost all of the carbs, you have to eat more fat and/or protein instead. The amount of protein in a low-carb eating plan does increase, but the real winner is fat.
Let’s be clear. “Fat” doesn’t mean “fattening.” We’re not talking about replacing bread, rice and fruit with hot-fudge sundaes and chocolate lava cake. We’re talking about a dramatic increase in the amount of healthy fats in the macronutrient mix.
That explains why heavy cream is very different than milk when it comes to a low-carbohydrate diet. When you look at the content of each, milk is 32% carbs and 48% fat. Cream is just 3% carbs, and a whopping 93% fat. It’s healthy fat, too. Heavy cream contains lots of vitamin A and Omega-3 fatty acids, key nutrients whose benefits range from fighting inflammation to fighting heart disease. (Heavy cream isn’t an “unlimited” food, though, because it’s very high in calories.)
Other healthy fats that are encouraged on low-carb diets: natural fats like butter, extra-virgin olive oil and coconut oil, fatty fish like salmon, tuna and mackerel, fatty cuts of meat and poultry, nuts, most types of seeds, eggs, and the best healthy fat of all, avocado.
You might think that fat is just the “default” macronutrient that replaces the carbs you’re cutting out of your diet. Not true. There are very good reasons why eating healthy fats can help you lose body fat.
- It takes much longer for the body to digest fat than carbs. That makes you feel full for a longer period of time and reduces your food intake.
- Studies show that dietary fat reduces levels of the hormone ghrelin, which makes you hungry.
- Carbs trigger the release of insulin, which helps turn glucose (blood sugar) into stored fat – but dietary fat doesn’t affect insulin release, so the body is free to burn its stored fat.
That’s true for all low-carb diet plans. But fat helps even more on a “very low-carb” diet like keto. It’s time to learn about the difference between the types of diets.
Types of Low-Carb Diets
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.
Low-Carb Diets and Ketosis
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.
Do Low-Carb Diets Really Work?
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.