What they are
Calories are a measure of the metabolizable chemical energy in a food or beverage.
What they do
In the most basic sense, the most important thing calories directly do is to help with body temperature regulation. Humans need to maintain their body temperature, within a pretty tight range, which is generally warmer than atmospheric conditions. The energy (i.e. calories) that is liberated by various chemical reactions within your body is what allows you to maintain your body temperature of approximately 98.6 Fahrenheit, or 37 Celcius.
In a more practical sense, energy balance drives changes in weight, and calories are a useful and common unit for quantifying energy consumption and expenditure. When you consume more total energy than you expend, your body stores the additional energy in the form of chemical bonds in fat, and to a lesser extent, glycogen (a complex carbohydrate primarily found in the liver and skeletal muscle tissue), and proteins. When you expend more total energy than you consume, your body breaks down fat, glycogen, and (to a lesser extent) proteins to liberate the energy stored in those chemical bonds, in order to meet its energetic needs. This is the primary process underpinning changes in body weight.
Calorie needs vary considerably based on your body size, body composition, age, sex, lifestyle, life circumstances, activity levels, and goals related to weight change. If you’re on a coached or collaborative program in MacroFactor, and you do a good job of diligently tracking your weight and food intake, your recommended calorie intake is just your calorie target on your current program.
Likelihood of tracking completeness: Very high
Virtually all foods in the MacroFactor database contain calorie information, so it should be easy to accurately track your calorie intake with consistent food logging.
For more on the likelihood of tracking completeness, check out this article.
Likelihood of insufficient intake: Very Low
The vast majority of people in developed countries are able to achieve sufficient energy intake, so a true energy deficiency is extremely uncommon, outside of severe eating disorders.
However, low energy availability and relative energy deficiency in sport (RED-S) would qualify as energy insufficiency. Low energy availability and RED-S are more common in individuals with greater total energy expenditure (especially in the form of endurance exercise), especially when energy expenditure quickly increases, or when an individual attempts to lose weight too quickly.
For more on nutrients with a greater likelihood of insufficient or excessive intake, check out this article.
Signs of deficiency/insufficiency
The classic signs of low energy availability and RED-S are a decrease in physical performance and energy levels, an increase in injury rates and mild illnesses, and decreases in libido (often coupled with menstrual cycle changes in female athletes) and rates of recovery from exercise. If this state persists, athletes can experience a decrease in bone mineral density, which often manifests in the form of stress fractures.
If you’re concerned that you’re experiencing low energy availability or RED-S, you should consult with a sports dietician.
In other populations, symptoms associated with low energy intake are generally mild, and are typically the result of targeting an aggressive rate of weight loss. Sharp increases in hunger, low energy levels, and brain fog are the most common signs. If you experience those symptoms, a decrease in your target rate of weight loss can help considerably.
If you’d like to read more about energy balance, you might enjoy this article from the knowledge base.