If you’ve been struggling with weight gain, the question “do calories matter?” has most likely crossed your mind once or twice.

Some authorities talk about being in a calorie deficit like it’s the golden ticket to weight loss. While others claim long-term fat loss has more to do with a whole food diet plan and your activity level than calorie counting.

And what if you’re following a low-carbohydrate diet? Does this affect whether or not you need to count calories?

There are a lot of opinions out there advising how to fight body fat, but there’s no better authority than science. So let’s dig in.  

What Are Calories?

A calorie is a measurement of energy. One calorie (or Kcal) is the amount of energy it takes to heat one kilogram of water by one degree Celsius. That’s a mouthful, but food scientists needed to find some way to quantify the energy in food — so there it is.

So when you refer to the calories in your food, you’re actually talking about the energy in your food.

Let’s break it down a bit:

Every macronutrient (protein, carb, fat) is composed of atoms, and each of those atoms is held together by energetic bonds. Different macronutrients take varying amounts of energy to be held together, so the calorie content of each macronutrient is different.

For instance[*]:

  • 1 gram of protein = 4 calories (4 units of energy)
  • 1 gram of carbohydrate- 4 calories (4 units of energy)
  • 1 gram of fat = 9 calories (9 units of energy)
  • 1 gram of alcohol = 7 calories (7 units of energy)

All day every day your body is using energy (AKA calories) to keep things running smoothly. In fact, the average adult burns somewhere between 1800 and 2600 calories per day[*]. This energy is either coming from the food you ate, or from your fat stores.

So when it comes to weight loss, how your body is using calories plays a considerable role.

The Role Of Hormones In Weight Loss

The goal of weight loss is to get your body into a place where it’s using your stored fat as fuel. If your body isn’t using fat as a source of fuel, then your stored fats just going to sit there. The trick is to figure out how you can eat, move, and live in a way that will maximize fat burning, and minimize fat storage.

What you eat, and the caloric breakdown of the specific foods you eat, plays a significant role in weight loss. But calories would be nothing, utterly useless, if you didn’t have hormones telling your body what to do with them.

While there are a myriad of hormones that play a role in the weight loss equation, the three biggies are insulin, glucagon, and leptin.


Your body runs a tight ship when it comes to fuel sources roaming around in the blood. It likes to maintain homeostasis with levels of fuel — not too much and no too little. To create this perfect balance it employs the help of two hormones, insulin, and glucagon.

When your blood sugar gets high insulin comes in to clean up shop. It regulates blood sugar levels by shuttling excess glucose into your cells to either be used as fuel or stored as fat. Insulin is sometimes known as the “fat storage hormone.”

Insulin is also antilipolytic—which means it works against the breakdown of fat. When insulin is high your body gets the message that there’s fuel to be burned, so leave those fat stores alone[*].

Put simply, when insulin is present in your blood you’re going to be storing more energy, and your capacity to burn fat is hampered.

But insulin alone isn’t the problem; it’s more of a symptom of the problem. The real issue is high levels of fuel (in the form of blood sugar), being present in your blood. Since insulin is released in response to blood glucose, if you keep your blood glucose low you’ll be keeping your insulin low.


Glucagon is the opposing force of insulin. It can only be released when insulin is low. These two have an interesting fuel burning vs. fuel storing dance. When glucose levels start to fall below a certain level, glucagon is released in the blood. The presence of glucagon triggers your liver to release stored glucose, and maintain blood glucose homeostasis[*]. This typically occurs between meals or during exercise when your blood glucose is being used up.  

However, when glucose is in short supply (like when you’re following a low-carb diet), glucagon has to search elsewhere for fuel to maintain your blood homeostasis. It does this by releasing fat from your fat cells, sending that fat to your liver, and converting it into ketones. Your tissues can then use those ketones for fuel, and all is well in the metabolic world[*][*].

So if high insulin means you store fat, and high glucagon means you burn fat, when it comes to weight loss you clearly want to keep insulin levels low.

The best way to do this? Avoid triggering an insulin response by avoiding high carbohydrate foods.


Another hormone worth mentioning is leptin. Leptin is a hormone that’s produced by your fat cells. It’s also known as the “satiety hormone” because it gives your body the signal that you have enough fuel, and you can stop eating. Its primary role is the regulation of energy in your body. It keeps an eye on how many calories you take in, how many calories you burn, and how much fat you have stored for later use.

Your fat cells basically use leptin as a messenger to send a signal to your brain saying, “we’re all set, we’re full, no need to keep consuming.”

It works the other way as well. When your fat stores are low, the opposite happens — you have less fat to talk to your brain, so it gets the message, “Hey, we’re running a little low on stored fuel here, let’s eat and bulk up these fat stores”[*].

So then shouldn’t people who are overweight have diminished appetites, due to high levels of fat tissue creating high levels of leptin? In theory yes, unless they have something called leptin resistance.

Leptin resistance happens when your body is making enough leptin, but your brain doesn’t see it. In other words, the message is being sent by your fat cells to your brain – but your brain isn’t getting the mail.

So your brain still thinks your body needs more fuel, for all it knows you’re starving. Dutifully, your hunger increases and you continue to eat, store fat, and the cycle repeats[*].

Why All Calories Are Not Created Equal

The Problem With The “Calories In Vs. Calorie Out” Approach To Weight Loss

For a long time people talked about weight loss as a simple “calories in, calories out” equation. The idea being that if you just burned more calories than you ate, you should lose weight.

In theory this makes sense, but in reality, it’s far too simplistic to apply to the complex machine that is your body.

Let’s take a look at a few reasons the old “calories in vs. calories out” paradigm doesn’t hold much water.

The Thermic Effect of Food

The thermic effect of food (TEF), is a concept that illustrates how much energy it takes for your body to break down certain foods.

For instance, when you consume protein, it’s much harder for your body to break down than carbohydrates. It takes more energy, and more calories are burned, so the thermic effect of protein is said to be high than that of carbohydrates[*].

In fact, the TEF for protein is 25%, meaning 25% of the calories you eat from a protein source actually go into breaking down that food. For carbohydrate, that number is only 8%.

So if you eat 100 calories of protein, 75 calories are left after digestion. If you eat 100 calories of carbohydrates, 92 calories are left after digestion.

Oxidative Priority

Another concept that exemplifies how all calories are not created equal is oxidative priority.

As mentioned earlier, your body runs a tight ship when it comes to the fuel in your blood. Researchers have coined the term “oxidative priority”, or “oxidative hierarchy” to explain how your body chooses which types of fuel to use first when there are several options present in the bloodstream[*]. Oxidation is just another way to say “fuel burning”.

The hierarchy goes like this:

As you can see, calories coming from different macronutrients create a vastly different metabolic effect.

Number one is pretty self-explanatory. Number two, however, takes a little more work.

If you want to avoid cravings, you need to look at what you’re eating. Different foods can have a significant effect on your satiety and cravings, and ultimately your resolve to stick to your diet.

Protein is well known for its ability to induce satiety. After eating a protein-rich meal, you will most likely feel more content and less likely to reach for a sugary snack. In fact, many successful dieters report increasing their protein intake to stave off cravings that might throw them off track[*][*][*].

In addition to its satiety-inducing effects, protein may also increase your body’s sensitivity to the hormone leptin. As a reminder — leptin is responsible for telling your brain that you are full, satisfied, and don’t need any more food[*].

Sugar, on the other hand, seems to trigger an addictive-like reaction in some people. The concept of “sugar addiction” has even been thrown around as one of the possible causes of obesity in the United States[*][*].

You can see how eating a 200 calorie snack coming from protein would have a much different effect on your diet goals than if you ate just as many calories coming from sugar.

Food Quality

A final point to make on the “why all calories are not created equal” topic is the concept of food quality.

Let’s say you eat two meals –they’re both protein-rich, have the same number of calories, the TEF and oxidative priority are equal, but the quality of the food is different.

  • Meal #1 is made up of organic chicken breast, sauteed kale, coconut oil, and spaghetti squash.
  • Meal #2 is a non-organic hot dog, a low-carb bun, and some sugar-free condiments sweetened with sucralose.

These two meals should have the same metabolic effect in your body, right?


When you consume calories that come from whole foods vs. processed foods you’re consuming a treasure trove of nutrients along with them. Whole foods are naturally rich in vitamins, minerals, and enzymes. All of these nutrients play a role in your metabolism and help keep your body running smoothly[*][*][*].

On the other hand, consuming calories coming from highly processed foods that are devoid of nutrients leaves your body feeling unsatisfied and wanting more. Not to mention the toll is takes to digest and absorb these foods without getting a nutrient boost in return.

Why Calories Do Matter on a Ketogenic Diet

If your goal is weight loss, then even when following a ketogenic diet you need to be aware of calories.

When you’re eating keto, you’ll notice a natural decrease in appetite, which is always helpful when you’re trying to cut back. Many people end up eating less because they feel more satisfied off less food, and are no longer fighting sugar cravings[*].

However, if you do end up eating more calories than your body needs — they’re still getting stored as fat. There’s just no way around this phenomenon.

The thermic effect of the food you eat will also continue to play a role when you’re in keto, and of course, the quality of those calories will always matter.

Can’t You Just Burn All the Calories You Eat?

Some people try to take matters into their own hands and burn off any extra calories they eat through exercise. In theory, this sounds like a good plan. “I ate an extra 200 calories, so I’ll burn off an extra 200 calories”.

The problem comes back to the complexity of your body, as well as the effort it takes to burn calories.

A 155-pound person doing high impact aerobics burns about 260 calories in 30 minutes[*]. That’s the equivalent of 3 tablespoons of nut butter, a standard protein bar, or 3 oz of steak. If one pound of fat equals 3500 calories, then you would have to do 7 hours of high impact aerobics to burn one pound of fat.  

As you can see, the numbers don’t add up.

In addition to this, research shows that the effect exercise has on calorie burning may be somewhat overblown — and diet cannot be ignored when it comes to weight loss[*].

Do Calories Matter on The Keto Diet?

In short- yes calories do matter on the keto diet. Although you’ll undoubtedly feel less hungry and will therefore need less food, a caloric deficit is still a piece of the weight loss puzzle.

If you don’t already know how many calories you should be consuming every day, use this calorie counting tool to determine your ideal caloric intake: Keto Macro Calculator.


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