The Maths Behind The Holiday Season Weight Gain

A Month of Mayhem.  No wonder we call December “Dizzy Tyd”, we really do get a bit dizzy trying to balance our lives. This article is a simple show of how one can put on some k’s during the festive season. I am going to use my metrics to make the maths easier to understand.

W – Weight: 76Kg
H – Height: 167cm
A – Age: 39
F – Body Fat % 30

BMR – Basal Metabolic Rate is the energy I require while I am awake, doing no activity and not eating. There are 3 equations used to estimate BMR, please don’t bother with the numbers unless you are really interested. All you have to notice is the difference. For my purposes I will use the Mifflin-St Jeor Equation and it estimates my BMR at 1614Cal (see other equations at the end of the article)

As soon as I start eating and exercising the numbers will start to increase, I will need extra energy to burn while exercising, performing daily activity and to digest the food I eat. When I don’t do much exercise and I just have 3 meals a day, my daily caloric requirement becomes 1.2 X 1614 (BMR) = 1936.

During the year I often exercise and my daily caloric requirement can go to 2200 – 3000 calories depending on the intensity and length of exercise. The most I have clocked was needing in excess of 12000Cal a day and that was from doing the 90Km Comrades marathon.

On days when one is active and eats well, the body tends to use the same number or more calories than one eats during the day. This means there is no need for storage (piling on the fat). Instead the body often uses the fat stores to bring energy requirement to a balance, meaning one will lose weight. Your body is intelligent like that.

Come December, and the troubles begin. We often bring our activity levels right down while increasing our consumption of calorie dense foods. So a person will spend 30 days without activity but eating like they need the calories. When one needs 1936 calories, but eats in excess of 2500 calories a day, there will be a surplus. The body is also smart in that regard; it puts surplus in storage. The best way to store energy in the body is…. yep you guessed it, fat.

Quick maths (illustrative purposes only)

Days: 30
Daily Calorie Surplus: 500Cal – 1000Cal
Total calorie surplus over 30 days: 15 000Cal – 30 000Cal
1g of fat provides: 9Cal.
If all the surplus calories got converted to fat, you would sit at 1,6Kg – 3,2Kg fat gain in 30 days.

Simply put, if you reduce the activity, remember to reduce the consumption of calories. The real purpose of food is nourishment, not entertainment. You are allowed to have fun but don’t get lost in the hype.

Happy holidays.

The Equations (more math)

Mifflin-St Jeor Equation:
For men: BMR = 10W + 6.25H – 5A + 5 (1613,75)
For women: BMR = 10W + 6.25H – 5A – 161


Revised Harris-Benedict Equation:
For men: BMR = 13.397W + 4.799H – 5.677A + 88.362 (1686.537)
For women: BMR = 9.247W + 3.098H – 4.330A + 447.593


Katch-McArdle Formula:
BMR = 370 + 21.6(1 – F)W (1519,12)