How Do We Gain Body Fat?

Are you someone who would like to lose a few pounds of fat or more? Have you been struggling with your weight on and off for years? Do you feel like you have been stuck for a long time, unable to move the scale down at all? Maybe it is time to take a step back and really think about how we actually gain body fat.


This first one is obvious to most of us. The whole health and fitness industry has been screaming this for decades. If you eat too much you will gain excess body fat. We are all well aware of this one by now. Did you know that there are 3500 calories in one pound of fat? So for you to gain one pound of fat, you would need a SURPLUS of 3500 calories over your TDEE (Total Daily Energy Expenditure) over the course of a few days or a week. (Don’t know what TDEE stands for? Check out this article about metabolism here!) 

So let’s use round numbers. Let’s say your body needs 2,000 calories a day to break even. If you eat 2,500 calories a day for a week, then you will have gained one pound of fat. As demonstrated below in Figure 1. This is an important thing to understand for individuals who worry about the daily and weekly fluctuations of their weight on the scale. It is very unlikely that you gained 5 pounds of fat on Thanksgiving day. You gained that fat over the course of a few weeks. And the extra pounds the day after Thanksgiving is likely just retained water.

Think about it, to gain 5 pounds of fat in a day you would need to have eaten 19,500 calories in a day. That is simply not possible, even if most people tried. Even professional athletes like Olympic swimmer Michael Phelps who do extreme amounts of exercise each day and as a result need to consume an outrageous amount of calories only get about 10,000 calories a day at most. Bottom line, you aren’t consuming enough calories to gain 5 pounds of fat on Thanksgiving 

Gaining weight from overeating comes with time. If you eat a few hundred calories over your TDEE daily, every day, over a month you will notice that you’ve gained a pound or two. Overeating and fat gain doesn’t happen with a few bad meals a month. It happens with a daily lifestyle of bad habits that add up.

Figure 1


This is less talked about, but, in my opinion, is a bigger issue than overeating. I know it might not seem to make any sense when you hear it because, as you know, it takes a surplus of calories to gain weight, but hear me out. Undereating is a problem!

Let’s talk about your TDEE, and pretend that you need 2,000 calories a day to break even. Now let’s pretend that you are only eating an average of 1,000 calories daily. Initially, you might lose fat due to the deficit. Over time, however, your metabolism slows down to adjust to your extremely low calorie intake.

Now maybe your TDEE is down to 1,500 due to metabolic adaptation. Previously you would have had to eat 2,500 calories a day to gain one pound of fat a week. Now if you eat just 2,000 calories a day, you will gain one pound of fat a week. This is what happens to many individuals who go on extreme calorie restrictive diets. These extreme diets lead to an inevitable rebound and yo-yo dieting.

The mentality of “eat less and move more” is driving a lot of well-meaning people to inadvertently slow down their metabolism and cause themselves to gain more weight in the long term. If you have been dieting for a long time, talk to our nutritionist to see if we can work with your calories and lifestyle to help improve your metabolism/ TDEE. See Figure 2 and 3 below for an example of this effect.

A word of hope, unless you were on the TV show “The Biggest Loser” (studies showed participants did long-term damage to their metabolism) then your metabolism isn’t damaged, it has just adapted. There are things you can do to bring your metabolism back up to the lean, mean, fat burning machine it’s meant to be. This is one of our staff’s favorite things to help our patients with!

Figure 2

Hormonal Issues

We are seeing a spike of hormonal problems leading to fat gain in the last decade. These issues range from PCOS and endometriosis in women to low testosterone in men. (To name a few) These are usually due to environmental factors and lifestyle variables.

Environmental hormone issues have been linked to plastics, artificial fragrance, and other chemicals in our lives. In the last 5 years alone there have been over 2,530 studies done linking plastics to endocrine disruptors! A few things you can do right away to improve your hormonal health is to:

While it might feel scary and overwhelming with all the environmental issues that affect our hormones. We can still control the lifestyle choices that can make or break us hormonally. Things like poor quality foods, too much caffeine, certain drugs, not drinking enough water, as well as other physiological stressors. If you know you are a high-stress person, you might be interested in reading this article on how stress makes us gain extra body fat.

Figure 3


We might see a family where the grandparents are overweight, the parents are overweight, and their kids are overweight. It is easy to see a family like this and just assume it must be their genetics.

I want you to think about this though. America is a melting pot of diverse genetics from around the world. Yet we still have a big issue of being overweight despite our genetic pool.

That overweight family has more than just their genetics in common. They also share a pantry and a similar lifestyle. Remember this, it’s not your genetics that makes you gain weight. It’s your lifestyle. An article published by Harvard Health talks about this and states that only a handful of genes have been shown to be key players in your predisposition to being overweight. At the end of the day, it still comes down to eating the appropriate calories for your energy demands.

To sum it up

  1. You need to eat the appropriate calories for your energy demand.
  2. If you are overeating you will gain weight quickly over a few months and years (not days).
  3. If you are undereating you will slow down your metabolism and cause yourself to rebound harder every time you go off your diet.
  4. If your hormones are not optimized, then it can make it almost impossible to lose fat.
  5. Your genetics are not a big enough concern to worry about. Pay attention to your lifestyle and focus on what you can control.

Are you interested in finding out how you can lose weight? Call our clinic today and we will get you started on our nutrition class and you’ll be on your way to losing weight, looking good, and feeling better in no time.