The short answer to this questions is NO.  You cannot directly calculate your increased calorie allowance based on increased exercise levels.

This is because the equation Calories In = Calories Out is not entirely accurate.

While it is true that if you eat significantly more Calories then your body burns per day, then you will store these Calories as fat and likely gain weight.  This is because of the Law of Thermodynamics, which states that energy is neither created nor destroyed.    In addition, if you eat significantly less Calories then you burn per day, in theory you should lose weight.

However, the problem is that not all Calories are created equally.

Foods are processed via different biological pathways, and have different effects on complex hormones in the body.

For example, 100 Calories of protein consumed are not processed by your body the same way that 100 Calories of carbohydrates consumed are processed.

When you eat 100 Calories of protein, your body uses between 20-30% of those Calories just to chew, swallow and digest the proteins.  Therefore you are left with a net of 70-80 Calories for your body to burn or store.  In addition, eating protein provides your body with amino acids, which form the building blocks to make more muscle.  This muscle in turn is then able to burn more fat and boost the metabolic rate.    The protein also stimulates your satiety center, so you will feel full and satisfied.

In contrast, when you eat 100 Calories of carbohydrates (we will use fructose in this example) it only takes about 5-10% of those calories  to digest the fructose.  Therefore you are left with a net of 90-95 Calories for your body to utilize.  If your liver has room, it will store the fructose ultimately as glycogen.  However, if your stores are glycogen are full in the liver, then the body will convert the carbohydrates to fat and store them.   In addition, fructose raises insulin levels, a hormone which ultimately promotes fat storage,  and has no effect on decreasing hunger hormone ghrelin.  Therefore, you will likely still be hungry.   Furthermore, fructose can lead to insulin resistance, and increase your cholesterol and triglyceride levels and increase abdominal obesity.

With regard to fat metabolism, it takes only 0-3% of total Calories consumed to process fat.   Therefore, 100 Calories of fat results in a net of 97-100 Calories to be burned or stored by the body.  It is important to understand however that not all fats are bad, and they body needs fat for survival and brain function.   Trans fats lead to inflammation and insulin resistance.  However, good fats, can decrease inflammation and promote cardiovascular health.

When you diet, and begin to cut Calories, your body thinks you are starving, and will therefore decrease your metabolic rate to conserve energy.   A recent study done by Pontzer and colleagues and published on Jan 28 in Current Biology, found that for “less active people, energy expenditure increased alongside increases in physical activity.  But at higher levels of activity, calorie burn plateaued. “The body has a metabolic set point, which it works very hard to maintain.

The take home message from this study is in order to lose weight, it is more effective to focus on calorie intake, rather then increase activity above a certain point.

Not only is it important to limit calorie intake, but it is also important to eat the right types of Calories, at the right times, in the right portions.  This is because a proper diet is can optimize your nutrition obtained from high quality foods.  This in turn, positively impacts your body and targets weight loss hormones rather then promoting hormones which signal the body to store weight.