Calories In, Calories Out (CICO)

As we touched on before, all weight loss/weight gain comes from the concept of 'Calories In, Calories Out'.

Think of your excess body fat as simply excess energy. When you are in a calorie surplus, your body will store excess energy as fat (or muscle - although at a very slow rate). Similarly, when you are in a calorie deficit, using up more than you take in, your body relies on fat stores (or sometimes your muscle tissue) to expend as energy instead.

Factors Affecting Calories Out

The body expends energy through various processes:

• Basal Metabolic Rate (BMR): Energy expended at rest for essential bodily functions.
• Thermic Effect of Food (TEF): Energy used for digesting, absorbing, and metabolizing food.
• Physical Activity: Energy expended through intentional exercise and daily movement.
• Non-Exercise Activity Thermogenesis (NEAT): Energy used for daily activities like walking, fidgeting, and standing.

All of these processes totalled up will comprise your Total Daily Energy Expenditure (TDEE). This will be wildly different for everyone, as everyone has different rates of metabolism, different levels of physical activity, etc etc.

Factors Affecting Calories In

The only way that you can intake calories is through your diet. So 'Calories In' is wholly dictated by the calories of the foods you consume.

CICO and Muscle Gain/Loss

Gaining or losing muscle, and gaining and losing weight, are two different things. Gaining or losing muscle comes about primarily due to protein intake and increased levels of Muscle Protein Synthesis (from training). Gaining and losing weight comes about primarily due to a calorie surplus or deficit. So how can we incorporate both to increase our muscle while decreasing our fat?

The truth is, unfortunately, for most people, you can't have your cake and eat it too.

People who have little to no experience in resistance training, and/or people with a large amount of excess body fat can perform what is called 'body recomposition', where they both lose body fat and gain lean muscle tissue. This is done by eating in a calorie deficit, while ensuring protein levels are very high, and training consistently.

For most people however, you will have to pick; either eating in a calorie surplus with the goal of building more muscle tissue, or in a deficit, with the goal of shedding excess body fat (and hopefully, holding onto existing tissue). This is what's known as 'bulking' or 'cutting' cycles.

Gaining muscle itself (a 'bulk') typically will require a small calorie surplus, typically about 200-500 calories above maintenance. This is sort of because the body does not prioritize the growth of new muscle tissue over other bodily processes. Thus, it needs to ensure that everything else is taken care of before it can delegate energy into new lean muscle. Note that eating in a calorie surplus of more than 200-500 calories does not 'speed up' the process of muscle growth, but rather will simply be converted to and stored as excess body fat.

Meanwhile, the process of shedding excess body fat(a 'cut') simply means to eat in a calorie deficit, while training consistently and eating large amounts of protein. This will offset muscle atrophy that may occur due to the body being in a state of using up its energy stores for daily expenditure, ensuring you retain all the muscle you had previously, while the body uses up fat stores.

Summary