Calories

Calories are the single most powerful nutritional variable influencing body weight, health, body composition, and sport performance.

What is a Calorie?

A calorie is a unit of measurement for energy. More exactly, it's the amount of energy in the form of heat that is required to raise the temperature of one kilogram of water from 14.5 to 15.5 degree Celsius.

As we defined it, the calorie is a very small unit of energy. When we talk about energy intake or expenditure, we typically refer to kilocalories.

One kilocalorie is equal to one thousand calories. You might also encounter kilojoules as a unit. One calorie is equal to 4.184 joules. One kilocalorie is equal to 4.184 kilojoules.

This is the scientific definition of calorie. Interesting, but not exaclty helpful when deciding what to eat for health and fitness.

Calories and Body Weight

In nutrition, calories measure the amount of energy we get from the food we eat. We can either use this energy or store it in our bodies.

If we consume exactly enough calories per day to meet our energy needs, body weight remains stable over time. If we consume less calories per day than we need, the body must break down its own tissues (most commonly fat) for the missing energy. This condition results in weight loss.

Conversely, if we take in more energy than we need, the body stores most of it as new tissue (most commonly fat) resulting in weight gain.

This concept is know as energy balance and is one of the single most important concepts in nutrition.

Calories and Health

Calories have a massive effect on health, and that's mostly because of their relationship with body weight. How much you weigh at a given height has probably the most important effect on your health.

If you weigh within the range of healthy weights for your height, it's likely that you're getting the right amount of calories you need to support health. Weighing much less or much more than that, however, might put your health at risk.

When chronically under-eating calories, body weight will eventually drop so low that health will begin to suffer. When you're chronically underweight, you lack the nutrients and energy to properly support your immune system. Also, muscle and bone reconstruction suffer.

Excess body weight (and especially body fat) is also a problem. The heavier you are beyond your healthy weight, and the longer you remain heavy, the more your health suffers.

Calories and Body Composition

Body composition describes how much muscle and fat your body is made of. Calories are the single most important factor in nutrition for altering body composition.

Your body is primed by millions of years of evolution to prepare itself for impending famine. So when extra calories are consumed, the body stores most of the excess energy as body fat to prepare for times of low food availability.

Another side effect of our evolution is that the body sees adding new muscle as a survival disadvantage. Muscles require more energy to build and maintain than fat. As a result, the body will not activate muscle growth until excess calories are consumed.

Improving body composition refers to getting leaner, more muscular or both. If your goal is fat loss, you'll need to generate a calorie deficit. In contrast, if your goal is muscle gain, you'll need to generate a calorie surplus.

Calories and Sport Performance

Calorie intake affects sport performance by mediating energy availability and facilitating recovery.

At the onset of exercise, blood glucose from recent food intake is the most readily available energy source. As training continues, glycogen stores in the muscles continue to provide energy to maintain performance. Glycogen stores in the liver act to moderate blood glucose levels as well. Fat stores contribute to energy release too, but at a much slower rate.

Calorie consumption affects all the energy pathways. Calories provide readily available blood glucose, build up glycogen stores in the muscles and liver, and build up fat stores in the adipose tissue over time.

In addition to providing energy for activity, calories also provide the energy to recover from training. Training for fitness involves damaging and rebuilding stronger tissues. When calories are unsufficient, the process will be slower and recovery will be incomplete.

Calorie Needs

Daily calorie needs can vary a lot from one person to the next. A number of factors contribute to this variation.

Some of these factors are:

• Body size
• Gender
• Height and body proportions
• Body fat percentage
• Genetic metabolic factors
• Training and lifestyle
• Stress levels

Conclusions

Calories are the single most powerful nutritional variable influencing body weight, health, body composition, and sport performance.

Calories are the main responsible of the total health effect of your diet because your body weight (and especially your body fat level) is so important to your health. They are also the most important factor in nutrition for improving body composition, sport performance and recovery from training.

Daily calorie needs can vary significantly both between and within individuals day to day.