Are you counting calories, avoiding fatty foods, and exercising every day, but your scale is so stuck on the same number, you're sure it must be broken? If you've been doing everything "right," maybe it's your diet - and not your scale - that needs a fix. Fortunately, there's a way to lose weight that's effective, sustainable, healthy and even enjoyable: low carb.
Here at Diet Doctor, one of our goals is to offer you guidance about confusing issues about health and nutrition. We strive to make this guidance trustworthy by backing it with evidence - and by explaining that evidence in ways that are easy to understand. Read on to learn why following a low-carb lifestyle can help you lose weight.
1. What is a low-carb/keto diet?
Carbohydrates are one of the three major nutrients found in food. Unlike protein and fat, which have other functions, their only role is providing energy for your body.
Low-carb diets - true to their name - contain very few carbohydrates (affectionately known as carbs), which are mostly found in sugary and starchy foods. These diets also provide adequate protein and more fat than a low-fat diet.
You'd have to be hiding from the internet altogether not to have heard about "keto diets," but that term is really meant for only the strictest form of a low-carb diet. LCHF (low-carb, high-fat) is another name for these diets. Hearing about other people and celebrities losing weight on low-carb diets might make them sound like they're just the latest fad, but there's a lot more to these diets than that.
2. Calories vs. carbs: what should I be counting?
To lose weight, you need to eat fewer calories than your body requires. True or false?
This statement is, in fact, true. Please don't shoot the messenger, though. Just because calories count, doesn't mean you have to count them! As we'll discuss, the way your body regulates its weight isn't as simple as adding and subtracting calories.
Calories are units of energy that allow your body to move, breathe, and play games on your smartphone. If you consume more calories than you burn, the excess energy will be stored as body fat. When you take in fewer calories than needed, your body will release some of its body fat stores to be used as energy. That's the whole point of dieting, right?
Yet trying to create a calorie deficit by intentionally restricting how much you eat often fails to achieve lasting weight loss. For one thing, it's often very hard to do long term. In fact, it may even contribute to weight gain over time, defeating the purpose of counting calories in the first place. It's increasingly clear there are many different things that influence how much we eat and whether the calories we consume are burned or stored. And one of those things is dietary carbs.
The not-so-secret trick is that reducing carb intake can trigger several changes in your body that may help it to burn more energy than it stores.
3. Eat less without counting calories? How does that work?
Rather than turning every meal into a math equation, carb restriction can help you automatically eat less without counting calories, in or out. Here's why:
Appetite suppression
Low-carb diets have a long and well-deserved reputation for decreasing appetite. Back in the 1950's, physician A.W. Pennington demonstrated that keeping carb intake very low allowed overweight people to lose weight without going hungry or deliberating restricting calories.
There are a number of reasons people might be less hungry on a low-carb diet. Lack of hunger when eating low-carb has been linked to ketosis, a metabolic state in which your body runs mainly on fat - at least some of which is body fat - and fat-like compounds called ketones. Studies clearly show that these diets reduce hunger.
Although researchers are still learning why low-carb diets reduce hunger, it seems to be connected to an increase in "fullness" hormones like CCK and a decrease in "hunger" hormones like ghrelin.
Also, a low-carb diet consists mostly of foods that make you feel full without spiking your blood sugar - I'm looking at you, protein, fat, and fiber-filled veggies. Plus, carbs are often a one-way ticket to a blood sugar roller coaster ride that can actually increase hunger.
For example, in a small study, 10 obese adults with type 2 diabetes who followed a non-calorie-restricted, very-low-carb diet ended up reducing their usual intake by 1,000 calories, on average - even though they were allowed all the fat and protein foods they wanted.
Fewer "empty" calories
Unlike essential fatty acids in fat and essential amino acids in protein, there are no "essential" components in carbs. Carbs are the decorative throw pillows of food: fun to have, but unnecessary for health.
Although they provide energy, the nutritional profiles of grains and many other foods high in carbs aren't really that impressive. But when you don't get enough essential nutrition, especially protein, your body may keep you reaching for more food in an attempt to satisfy those needs.
By contrast, when you eat mainly fish, eggs, cheese, and other high-quality foods, you can end up meeting those essential nutrient needs more easily. Your body might then feel satisfied with fewer calories, and less likely to send you snooping around for snacks every 30 minutes.
Reduced food reward
For many people, eating sweets and other refined carbs in processed foods can light up reward centers in the brain like a pinball machine. This can lead to cravings and can make it hard to eat "just one" of anything sugary or starchy.
But just because a real-foods, low-carb diet may reduce "food reward" cravings doesn't mean a low-carb diet doesn't include food that is rewarding in other ways! A low-carb diet includes many tasty, satisfying foods while discouraging those known to overactivate this food reward system.
Also, eating nourishing low-carb meals may help you feel pleasantly full and ready to move on when you're done, rather than wanting "just one more bite" (and maybe a nap afterwards).
4. Burning more calories without extra exercise
Although controversial and not yet accepted as settled science by all experts, there's high-quality research suggesting that low-carb diets can help you burn more calories. This might help you maintain lost weight.
After losing weight, many people experience a decrease in their metabolic rate. It seems completely unfair, but our bodies may not be designed to lose weight. Instead, they may decide we are in the middle of a great famine (despite passing 24-hour fast food joints every few miles!) and therefore start to slow down our metabolic rate, so we can use less fuel until the famine is over. The end result is that we have to eat even fewer calories if we want to maintain our weight loss. See what I mean? It's completely unfair!
But don't despair. There's some interesting research suggesting that this metabolic slow-down can be minimized with low-carb nutrition.
Two studies
In a 2012 study, 21 adults who'd lost weight on a calorie-restricted diet were shown to burn more calories during weight maintenance when they followed a low-carb diet compared to a low-fat diet - an average of around 300 calories per day more, in fact. This finding has been referred to as low-carb's "metabolic advantage."
According to Professor David Ludwig, one of the Harvard professors who conducted the study, this advantage "would equal the number of calories typically burned in an hour of moderate-intensity physical activity."
More recently, a similar but much larger study in 164 people appeared to confirm this effect, with participants who'd previously lost weight burning anywhere from 200 to nearly 500 more calories per day on a low-carb maintenance diet compared to a high-carb or moderate-carb maintenance diet.
You may want to exercise for other reasons. But on low carb you hopefully don't have to spend an extra hour on the treadmill just to avoid regaining the weight you've lost.
Insulin is a major player
Insulin, a hormone produced by your pancreas, has several important functions, including moving glucose (sugar) out of your blood and into your cells and helping you build and maintain muscle.
When levels are elevated, insulin also directs your body to store any excess calories as fat. Again, this is helpful if there's a famine right around the corner, but not so helpful when instead it's a 24-hour Taco Bell.
Eating a low-carb diet is a powerful way to reduce your insulin levels in addition to your total calorie intake. This combination allows your body to more easily use stored body fat for energy, which means: fat loss. During maintenance, though, it means you can usually increase your calorie levels somewhat without regaining weight. At that point, your body will burn dietary fat instead of body fat.
5. Show me the science
Although low-carb diets are still sometimes characterized as a "fad," they've been studied as a tool for weight loss for decades.
The most recent studies show a low-carb approach to be at least as effective as - and often clearly superior to - low-fat and calorie-restricted diets for losing weight. What's more, they nearly always lead to lower blood sugar, lower blood pressure, and other health improvements, regardless of what happens weight-wise.
Get ready, because here comes the serious science stuff. While it may not be that exciting, it is important to see what the evidence says, so stay with us!
Results of systematic reviews of RCTs
Experts consider randomized controlled trials (RCTs) to be the highest-quality research and the "gold standard" for evidence. Systematic reviews and meta-analyses of these RCTs are graded as the strongest, most rigorous evidence.
Researchers set a high standard - such as focusing only on long-term studies - and exclude any studies that don't meet it, such as studies lasting less than 12 weeks. Then they analyze results from studies all sharing these same high standards.
Within the past five years, several systematic reviews of RCTs comparing low-carb diets to low-fat diets have concluded that low carb results in greater weight loss overall:
The last review was limited to RCTs lasting at least 12 months, in order to determine whether very-low-carb diets or low-fat diets were more effective for weight loss long term. Again, low-carb was the winner.
In some trials, weight loss outcomes for low-carb or low-fat diets may differ very little, while changes in body composition are more pronounced - especially when very-low-carb diets are analyzed separately from diets with more modest carb restriction. For instance, one systematic review of 15 RCTs concluded that people who consume diets containing less than 50 grams of carbs per day seem to achieve greater fat loss than those who eat low-fat or low-carb diets containing more than 50 grams of carbs per day.
This is a good reminder that the scale doesn't tell the whole story! We can learn much more by following body composition.
About individual studies
Although experts think systematic reviews of RCTs are the strongest level of evidence, these reviews can't provide details about what happened in each study. Also, the outcomes may not look as impressive when averaged among many different studies.
If we take a look at some individual low-carb weight loss studies, we can learn a little more about the diets people followed and the results they achieved.
RCTs
In a two-year trial, 322 overweight adults were randomly assigned to follow a Mediterranean diet, a low-fat diet, or a low-carb diet. Those in the low-carb group consumed 20 grams of carbs per day for the first two months, which was gradually increased to as much as 120 grams of carbs, depending on each person's weight loss and maintenance goals. Among those who completed the study, the low-carb group lost the most weight. And here is the kicker. They ate as much low-carb food as they wanted. No restrictions! This was compared to the other groups, who had to purposely restrict their calories.
In this study, 148 overweight men and women were randomly assigned to consume a low-carb diet (less than 40 grams per day) or a low-fat diet (less than 30% of daily calories per day) for one year. Neither group was asked to restrict calories. In addition to losing 7.7 lbs (3.5 kg) more than the low-fat group, the low-carb group also had greater improvements in several heart disease risk factors.
One of the most well-known weight-loss trials involved randomly assigning overweight women to follow either a low-carb (Atkins), moderate-carb (Zone), low-fat (Ornish), or low-calorie, portion-controlled (LEARN) diet for one year. The Zone and LEARN diets had specific calorie restriction goals; the Atkins and Ornish diets did not. The low-carb group was instructed to eat 20 grams per day initially and gradually increase their carb intake to 50 grams or less per day.
By the end of the study, the women in the low-carb group had lost twice as much weight (an average of 10.3 lbs or 4.7 kg) as those in the Ornish and LEARN groups and nearly three times as much as those in the Zone group.
All of the results mentioned above are based on group averages, so your own mileage may vary. But in general, it is safe to say that low-carb diets outperform low-fat, calorie-restricted diets for most people.
Non-randomized trials
Evidence from non-randomized, non-controlled trials isn't as strong as RCT evidence, but these studies can provide helpful "real world" information about following a certain way of eating. For instance, sometimes these studies allow participants to select between two types of diets. If you're allowed to choose your own diet, you'll probably be more likely to stick with it, enjoy it, and achieve better results.
Adults enrolled in an ongoing study at Virta Health were given the choice to follow a very-low-carb diet that included frequent nutrition coaching or to receive standard diabetes care. After two years, those who selected the low-carb intervention and remained in the study had lost an average of 26 pounds (11.9 kg). Three-quarters of the group had reduced their body weight by 5% or more, in addition to improving their blood sugar control.
The results above are all impressive in their own right. But here are some other dramatic weight loss outcomes, although they did not have a self-select option or a control group.
In 2011, researchers studied the effects of a 12-week ketogenic diet in 22 people with metabolic syndrome. The diet provided less than 30 grams of carbs per day in the form of nonstarchy vegetables. By the end of the study, participants had lost an average of 32 pounds (14.5 kg). That's impressive, but what is even more important is that all of them no longer met the criteria for metabolic syndrome due to significant improvements in waist circumference, blood pressure, lipids, and fasting blood sugar.
In a slightly older, larger study, 83 obese adults followed a ketogenic diet restricted to less than 30 grams of carbs per day. After 24 weeks on the diet, participants had lost 31.5 pounds (14.3 kg), on average. They also achieved a number of health improvements, including lower triglycerides, LDL cholesterol and blood sugar, and higher HDL cholesterol.
Compliance and intention-to-treat studies
Ideally, all participants follow their assigned diet until the end of the study. However, this rarely, if ever, happens. Noncompliance in diet studies is very common, as is dropping out altogether. Traditionally, researchers report results for those who follow the diet they're instructed to eat and complete the trial. However, this practice can set up overly optimistic expectations for outcomes in real life, where many people find it difficult to stick to a diet.
In order to address this issue, researchers often conduct intention-to-treat (ITT) analyses of RCTs in which they report data for everyone, including those who didn't follow the diet they were assigned to, dropped out of the study, or otherwise didn't follow the study protocols.
However, ITT analysis can end up underestimating weight loss and other benefits that occur in people who do follow the dietary advice they've been given. In fairness, this applies to both low-carb and low-fat studies - and compliance is roughly equal for both diets.
We know dietary preferences vary a lot among different people. If a certain diet isn't a good fit for someone - if it feels hard to stick to or if weight loss is very slow - it's likely that the person won't end up following the diet.
Fortunately, low-carb diets are a good fit for many - and this may very well include you.
5. Summary
Let's briefly review the features and benefits of low-carb diets for weight loss:
- Delicious, nourishing foods that help you feel full and satisfied while eating less
- Weight loss at your own pace without consciously restricting calories
- Freedom from the "food reward" cycle triggered by high-carb foods
- Potential long-term health benefits
Why not try a low-carb diet on for size?
