Carbs vs. Calories - Which is More Important?

What You Need to Know About Losing Weight

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Have you seen headlines such as these?

"5 Ways to Save 100 Calories"

"Lower Your Breakfast Calories" (by throwing away the most nutritious part of the egg)

"6 Easy Ways to Lose 2 Pounds Per Week"

We are surrounded by information about calories, and emphasis on calories. Soon, our nutrition labels will feature a very large font for calorie information, because, you know, that's the most important thing we can know about a food.


On the other hand, people on low-carb diets generally do not count calories, and yet they lose weight. Does this mean that calories don't count? Is there value at all in paying attention to calories? There are legitimate issues to consider on both sides of this question. Here are some questions I get asked about this, and some different ways to think about the calories vs carbs conundrum.

Doesn't Research Show that Cutting Carbs and Calories Produce About the Same Weight Loss?

When you take a random group of people, randomly assign them to different diets, and follow them for a year, generally at the end the average weight loss is not that much different; it's somewhere between five and ten pounds. The low-carb group almost always loses more than low-fat or other groups, and almost always also has a greater improvement in other health parameters, such as belly fat, blood glucose, and blood lipids.

And yet, we often find that within each of the different diet groups in these studies there is a tremendous amount of variation in how much weight the participants lost. Most importantly, if the researchers look at who benefits from each diet, that turns out to be not so random after all. Generally, the people who are insulin resistant are more likely to respond positively to a diet lower in carbohydrate.

This brings us to an important question:

Are You a Random Person, or a Specific Person?

The "gold standard" for medical studies is that the participants are randomly assigned to the study groups. But what if there are groups of people within the general population who respond differently? What if some of them actually respond in opposite ways? If a cancer drug makes some people a lot better, but others a lot worse, the average might be "no difference," which obscures the truth for both of these groups of people.

At this point, over half of the adult population in the United States is insulin resistant, that is, they are somewhere on the diabetes spectrum. Many of these people do not show much outward sign of this , but this is the group which is more likely to respond to carbohydrate reduction.

How Can It Be That People Lose Weight Without Counting Calories?

To traditional calorie counters, this is one of the mental stumbling blocks. It really defies their imaginations. To lose weight, you have to consume fewer calories, right? It can't possibly make a difference where those calories come from.

They are half-right. To lose weight, we have to consume fewer calories. But the reason focusing on carbs works is deceptively simple: people on low-carb diets consume fewer calories because they aren't as hungry.

We know that eating carbs, especially refined carbs, which are more glycemic, leave people hungrier than eating protein and fat. This probably is the main reason that people lose weight on low-carb diets, and why people get so excited when they make this discovery.

The next question is what is going on in our bodies that makes us less hungry on a lower-carb diet.  There is preliminary evidence that this has to do with so-called hunger hormones like ghrelin and leptin, but further research is needed to confirm this.

What about low-calorie diets? These are also lower in carbs, in general (because they are lower in everything), but people eventually are going to be hungrier when they cut calories as opposed to cutting carbs.

  Partly, this is because cutting calories tend to encourage cutting down on fats (because fats have a lot of calories) and eating more carbs.  Eating a low-fat, high-carb diet is what got many of us in the overweight condition we are in, so we do need to avoid that.

What About People Who Are Not Insulin Resistant?

People who are insulin sensitive are more likely to be able to lose weight successfully by cutting calories. I think that this is probably partly simply because in general they have less weight to lose.

Unless something goes wrong (such as insulin resistance) our bodies tend to stay within a weight range without a lot of effort. This range varies from person to person, but it is generally thought to be around five to seven percent of body weight, which is about 7-12 pounds for a 150-pound person. Probably for most people who don't want to go below that range, playing with the number of calories they are eating can be helpful in keeping them at the lower end of their body's comfort range.

By the way, this is how the bodies of human beings, until very recently, have regulated body fat very efficiently. The average adult takes in almost three quarters of a million calories per year, and yet people's body weight stayed relatively stable without any math whatsoever. Stable, that is, unless something goes wrong, as it has in the last few decades when obesity rates began to rise.

Problems With Calorie Counting: Calories In Vs Calories Out

There are certainly some people who have success with calorie counting, but that path is fraught with inaccuracies, difficulties, and other traps. I'm only going to touch on them here, but rest assured that the simple equation you often hear about creating a calorie deficit by making sure fewer calories go in than are expended is not as simple as it sounds.

Issues with the "Calories In" Side of the Equation

The number of calories a food contains is actually difficult to pin down. Methods of measuring calories used vary in accuracy. Any given peach probably could have a different calorie count than its neighbor on the same branch due to differences in ripeness, and different again than a different variety of peach. Raw foods often have fewer available calories than cooked ones. Canned beans have less resistant starch than dried beans you cook yourself. And on and on. Food labels can legally be 20% off in either direction.

In addition, our bodies process foods differently. It's fascinating to look at the large ranges in studies of the glycemic index of different foods - the same food will send some people's blood glucose way higher than others. The bacteria in our guts is turning out to play a role in how our food is absorbed and in other ways our bodies process foods.

Also, unless we are very very careful in our measurements, we can be quite far off in our calorie estimates of what we are eating.

Issues With the "Calories Out" Side of the Equation

Guessing how many calories people expend is actually harder to know than guessing how many they are taking in.

In one study the researchers overfed people of normal weight by 1,000 calories per day for eight weeks without changing their exercise programs. They "should" have each gained 16 pounds. The actual weight gain was anywhere from less than a pound to a little over nine pounds.

Why? Some of it was probably genetics. But a lot of it was chalked up to the fact that people simply spontaneously starting moving more (some more than others). This was dubbed NEAT (non-exercise activity thermogenesis) and turns out to be one way that our bodies use to regulate our weight. In the same study, they underfed overweight and obese people who, naturally, cooperated by spontaneously moving less.

Other factors that affect the amount of calories we expend compared to our neighbor are genetic factors such as the FTO gene, our age (even healthy men in their 20's have been shown to have an age difference in how many calories are used doing the same activity), size, sleep, the amount of brown fat we carry, and other factors.

One of those other factors is metabolism, and one of the things that really affects that is weight loss. In an interesting study, they took people who had lost weight on a low-calorie diet. Then they put each person on three different maintenance diets, one after the other, and measured how many calories their bodies burned. It turned out that the diet a person was on made a huge difference in the amount of energy their bodies were using: when people were following a low-carb maintenance diet, their bodies burned 300 calories per day more than when they were following a low-fat maintenance diet.

Other Issues with Calorie Counting

All this doesn't even touch upon dealing with chronic hunger if you want to get to a lower weight than your body "wants" you to. (To be fair, at some point many low-carbers who want to lose a lot of weight will also run up against this, but they will probably be at a lower weight and healthier than if they had chosen the calorie-counting route.)

No wonder people I know who have successfully kept off (for at least five years) a substantial amount of weight by focusing on calories alone have one thing in common. Ready for the secret? None of them worked full-time (and raising children definitely counts as full-time work). That's right, fighting your physiology each and every hour of each and every day is a full-time job. It takes a pile of physical and mental energy, and doesn't leave room for a great deal else.

The Bottom Line

At this point, there is enough evidence that most people who want to lose weight should first try carbohydrate reduction and see what happens, as it carries proven health benefits along with weight loss, and once they get used to it, people tend to really really like it.


Ebbeling, CB et al. Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance. JAMA. 2012;307(24):2627-2634.

Levine, JA, et al Role of Nonexercise Activity Thermogenesis in Resistance to Fat Gain in Humans. Science. 1999 Jan 8;283(5399):212-4.

Sackner-Bernstein J, Kanter D., Kaul S. Dietary Intervention for Overweight and Obese Adults: Comparison of Low-Carbohydrate and Low-Fat Diets. A Meta-Analysis. PLoS One. 2015 Oct 20;10(10):e0139817.

Urban LE, Dallal GE et al The accuracy of stated energy contents of reduced-energy, commercially prepared foods. Journal of the American Dietetic Association 2010. 110(1):116-123.