Calories in, calories out. For athletes who aren't losing the fat that they want to lose, it's a term they often hear. Ask around for fat loss (or muscle gain) advice, and that’s what you’re likely to hear over and over. But does calorie counting work?

CICO (as this concept is usually abbreviated), is the basis for most fad diets. You're told that if you eat fewer calories, you'll lose weight, and if you eat more calories, you'll gain weight. However, not everyone agrees with this. The calorie theory of overall weight and body composition change does get periodically challenged, most recently by low-carbohydrate fans who blame insulin for fat gain.

Related: 6 Tips to Create a Perfect Day of Eating for Fat Loss

So that raises two questions: First, is changing caloric intake the only — or at least the primary — mechanism behind body composition change? And if it is, does that mean that you need to consistently count calories?

Does Calorie Counting Work for Fat Loss and Body Recomposition?

Most changes in weight and body composition are about calorie balance.

To lose mass without cutting back on calorie intake, you would need to do one of two things: lose water weight (which isn’t fat loss), or excrete fat or glucose un-metabolized. In other words, you’d need to be peeing out oil or sugar — in large quantities — and this doesn’t happen (not even in small quantities).

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To gain muscle without a calorie surplus, you would need to either gain water weight or build muscle while losing fat at the same time. Simultaneous fat loss and muscle growth is possible up to a point. (It typically does happen to novice trainees, but it becomes progressively more difficult the more muscle and less fat you have.)

Related: This Man Completely Recomposed His Body in Just Months. Here's How.

Barring those possibilities, losing fat and gaining muscle both rely heavily on caloric balance. Getting leaner requires cutting calories, and gaining muscle requires eating more. People often become overweight because they consume more calories than they burn, regardless of what kind of food they're eating or which type of activity they use to burn calories.

Note that many studies have found that people who cut calories fail to lose fat, but there’s a big caveat here: all of these studies asked the subjects to self-report their calorie intake and assumed those reports were accurate. However, people routinely underestimate their caloric intake by 20% or more. When calorie intake and expenditure are tracked in a lab setting, the findings of the study confirm that overall body weight change (including fat loss and muscle gain) is mostly a matter of calories in, calories out.

In short, caloric intake is the primary — but not only — mechanism behind body weight change. To lose fat, you need to eat fewer calories, and to gain muscle, you probably need to eat more calories.

Can You Lose Fat or Gain Muscle Without Counting Calories?

Yes, and athletes do it all of the time. While some may choose to adhere to specific meal plans such as plant-based eating, veganism, or Paleo, consistency really is key when it comes to fat loss, muscle gain, and optimal performance.

Related: 5 Reasons That Spartans Eat Whole Food-Fueled Meal Plans

If you don’t count calories, what you need to do instead is implement rules: rules about what kinds of foods you eat, when you eat, and roughly how big each of your meals will be. This approach yields similar results to calorie counting, according to research. That is, not only do both approaches tend to produce a similar amount of fat loss, but they also tend to lead people to make similar changes in what and how they eat. They reach the same destination by a different route.

Alternatives to Calorie Counting (and Why They Work)

Even if you don’t count calories, keep in mind that you still need to eat fewer calories to lose fat and more calories to gain muscle. There are many specific nutritional rules that you could implement that would help you gain or lose mass, but only a few underlying principles behind those rules.

6 Alternatives to "Counting Calories"

1. Reducing Caloric Density

To lose fat, you can eat less calorically-dense foods: beans instead of bread, or lean meat instead of fatty meat, for example.

2. Changing the Order in Which You Eat

You can eat fewer calories by filling up on low-calorie foods like vegetables first, or eat carbohydrate-heavy foods first, protein sources second, and vegetables last to put on a few pounds.

3. Meeting Your Micronutrient Needs

Some hunger is driven by the need for micronutrients, rather than by the need for more calories. So, eating foods with more vitamins and minerals will not only make you healthier, but it will also make you less hungry.

Related: These 5 Vitamin and Recovery Supplements Will Boost Your Energy

4. Adding More Food Variety ...

When you have a greater variety of foods and flavors present in any given meal, you’ll eat more. This can help you accumulate the calories you need to build more muscle. 

5. ... or Cutting Down on Variety

Cutting down on variety is sheer mindfulness that reduces your appetite, so you'll end up eating less on your own. Following any strict meal plan at all makes you think harder about what you put into your mouth and your body. When you eat mindfully, you’ll tend to make healthier food choices even without specific rules telling you to do so. 

Related: How to Start a Food Journal That Turns Motivation Into Discipline

6. Calorie Cycling

You can build more muscle and lose more fat by eating a disproportionate number of your calories in the 12–24 hours following a weight training workout, and fewer calories outside that window.

The Bottom Line: Does Calorie Counting Work?

To sum up, counting calories can be a solid option. In my opinion, everyone should do it for at least a short while — even if they don’t want to keep doing it long-term — to teach themselves how to at least estimate calories more accurately. If you face the problem of not seeing results or training progress despite adhering to your meal plan, this can be a solid starting point.

Related: 5 Ways to Put on 10 Pounds of Lean Muscle FAST

But it isn’t the only option. Broadly speaking, there are at least four ways for people to lose fat and/or gain muscle:

• Count calories. Eat less to lose fat, and eat more to gain muscle.
• Follow a diet that uses rules about what to eat, and possibly also when to eat.
• Eat a consistent, whole-food-based meal plan with three to six simple rules that cause you to eat less (or more if bulking) without needing to count calories.
• Build habits that cause you to eat more mindfully, so that you’ll make healthier food choices without ever having to follow a fad diet.