Exactly How Much Should I Eat? (The Scientific Approach)
If you are a healthy person (i.e. not in The Metabolic Shit Hole) your hormones should be in check, your menstrual cycle should be normal, and you should be sleeping well. To maintain this health it is important you consume enough calories. If you don’t eat enough calories you could cause some potentially very serious health issues. Notice I use the word “maintain”. This article is dedicated to helping you figure out your “Maintenance Calories”. In other words the normal amount of calories you should eat in a day to maintain a healthy body.
To begin with at a bare minimum, it is essential that you keep your body in a happy place while not sending hormones off track. This is attained by keeping your caloric intake above the “critical threshold” which is 13.6 cal/lbs LBM (lean body mass) or 30 cal/kg LBM. Keeping your calories above this threshold helps maintain something called an energy balance. If the energy balance goes below 11.3 cal/lbs LBM or 24 cal/kg LBM , the result is a negative effect on hormone balance and bone density. As a side note the bone density threshold is 11.3 cal/lbs LBM and the menstrual cycle threshold is 13.6 cal/lbs LBM, for adequate intake it is 20 cal/lbs LBM. If you go below threshold there is a danger of real damage being done.
Beyond this it difficult to determine how many calories each person needs on a day to day basis, due to the variability of activity on different days.
When determining how many calories you should eat you need to pay attention to four main factors:
a) Basil metabolic rate (BMR): For the BMR (Basil Metabolic Rate) there are calculations that you can use like this one from Bodybuilding.com(https://www.bodybuilding.com/fun/bmr_calculator.htm).
You can find others online, but they may not be terribly accurate because these equations tend to only work for women with a certain percentage of body fat.
When body fat is too high or too low, these numbers can be off.
There is also an equation that requires body fat percentage, from Lyle McDonald, that is more accurate if you are someone with very high or very low body fat percentages. His equation is below:
RMR= (12 calories multiplied by Lean Body Mass in lbs) + (2 calories multiplied by fat mass in lbs)
RMR (26.4 calories multiplied by LBM in kg) + (4.4 multiplied by fat mass in kg)
Example Of BMR Calculation:
Take a 135 pound female with 20% body fat. That means lean body mass would 105 pounds and fat mass would be 27 pounds
That means for RMR the numbers look like:
(12 calories multiplied by 105) + (2 calories multiplied by 27) = 1,260 calories + 54 calories = 1,314 calories
This number is approximately accurate for the number of calories burned at complete rest.
b) Thermogenic effect of food: The thermogenic effect of food is so small (around 10% of overall calories) that we will not worry about calculating these here
c) Thermogenic effect of non-exercise activity: The calories burned throughout the day need to be added in as well. These numbers can differ greatly between different women and also from day to day.
To determine your daily activity, you can use the following multiplication chart”:
“Sedentary”: Activity Level Factor = 1.2
“Lightly Active”: Activity Level Factor = 1.3-1.4
“Moderately Active”: Activity Level Factor = 1.5-1.6
“Very Active”: Activity Level Factor = 1.7
“Extremely Active”: Activity Level Factor = 1.8-1.9
You can take these numbers and multiply them with your calories.
Example From Above:
1,314 calories multiplied by 1.7 (“very active”) = 2,233.8
d) Thermogenic effect of Exercise Activity: You also need to add exercise calories to the total. This can also get complicated, especially with high level endurance athletes who complete long and slow workouts that can burn up to 2,000 calories one day and on other days complete shorter workouts that only burn 800 calories. These individuals would need to calculate their “calories burned” daily to ensure they are eating enough to support their training. Those who do light workouts such as powerlifting, Olympic lifting or “general training” in the gym may only need to add 200-500 calories daily for their workout (1 – 2.5 hours).
Using the first three attributes we arrived at a total of 2,233.8 calories. Let’s say a person burned 500 calories during exercise. They’d need 2733.8 calories daily.
This is a great way to figure out where to start for “Maintenance Calories”. If you are calculating these correctly, your weight should be maintained and you should stay in a happy and healthy place. Notice also the similarities between the numbers calculated in this article and my article “Exactly How Much Should I Eat? (Layman’s Version). If you don’t want to go through all the science to calculate calories go check out that article.