Genetics, Weight Gain and Weight Loss

Genetics and Obesity 300x283 Genetics, Weight Gain and Weight LossIf there is one thing I see all too often, it is “fat shaming.”  Most other prejudices in this country are known to be discouraged, but when it comes to blaming someone for their weight, it’s like we’re given free rein to say mean things.  Now don’t get me wrong, most people don’t eat very healthy in this country and most people could use more exercise, but here’s the thing, this applies to most people.  It applies equally well to skinny individuals as it does to overweight individuals and often times, the person’s genes are the main determinant of the bashing.

For example, one of my biggest pet peeves when I’m talking to someone and they see a “big” person (who they don’t know), and ask, “How could they let themselves get so fat?”  They are implying that these people must be both gluttonous and lazy.  They must overeat “all the time” and must not really care about their health.  I hate this comment, because it’s short-sighted and generally ignorant.  Sure some “big” people eat a ton and are lazy, but so are skinny people.  In fact, I’ve known many more skinny people who don’t give a crap about their health, who eat like crap and haven’t seen the inside of a gym in over a decade, than I have “big” people who don’t care about their health or what they’re eating.

Most people who are overweight or obese are usually one of three things:
1 – Overly and acutely aware of their weight, hate it and are constantly doing something about it.

2 – Feel a sense of helplessness and uncomfortableness since they have usually tried more diets than the average individual (research shows that in some groups, an average of 20 or more diets) and the weight usually comes back.  From that, they feel both helpless and either give up or beat themselves up for not sticking to a diet that is very hard or virtually impossible for nearly anyone to maintain.

3 – Have accepted themselves and do their best.

This last group is by far the smallest of these three groups and most people who are overweight are a combination of 2 or more of the above.

I literally could write a book on all of the differences that cause people to gain and lose weight at different rates as there are about 30 factors that contribute to weight gain and loss.  In fact, research has shown that a person’s weight is anywhere from 50-65% determined by genetics.  This is like going into a test and more than half your grade is completely out of your control.  Try to get an “A” every time you take a test in a situation like that.  Well, that’s what weight gain and loss really is.  Some people can lose it easier than others, while others struggle to lose 5 pounds in 3 months despite vigorous exercise(2nd study highlighted).  The rest of this article highlights some research showing how our genetics control a large portion of both weight gain and loss between individuals.

Over-Eating, Weight Gain and Genetics

Research when it comes to over-eating studies can get quite intense sometimes.  For example, in 1990, Canadian researcher Claude Bouchard and colleagues found 12 identical twins and had them move into a facility so that they could control all of their food intake and exercise (which they weren’t supposed to do).  During the 100 day study, all of the pairs of twins had to eat an extra 1,000 calories a day, 6 out of 7 days of the week.  This may seem like a fun challenge to some of you, but if you’ve ever felt super-stuffed after a Thanksgiving meal, imagine doing that, every day from that Thanksgiving until March 1st the following year.  Every once in a while eating a bit more can feel like a good time.  Every day, not so much.

Knowing how hard it is to constantly overeat, this was not an assignment the researchers left idly to the participants in the study.  Instead, they prepared all of the food and had them supervised while they ate all of the food served.  During those 100 days, average weight gain was about 18 pounds.  Averages though, do not show the individual variation within the study.

The interesting part of the study was that despite the controlled environment (preparing and tracking of all food eaten), weight gain ranged from just 9 pounds to over 29 pounds in 100 days (over 3 months of vastly overeating).  To put this in perspective, this means some of the participants were gaining 3 pounds of weight in just 10 days whereas others were gaining 3 pounds in a whole month. This study really was one of the best controlled studies which showed how genes can play a huge role in how easy it is for some people to gain weight versus others.  This genetic link was highlighted as the twin brothers were close in weight to each other, whereas the differences in weight between the groups of twins was huge.

Exercise, Weight Loss and Genetics

More research by Bouchard, published the following year, highlighted how exercise and one’s response to weight loss with exercise was also influenced by genetics.  In this study, he had 7 pairs of twins live in a facility where their diet was controlled again throughout the duration of the 90+ days.  This time though the pairs of twins had to complete two bouts of exercise on a stationary bike, burning a total of 1,000 calories per day.  This time, the average weight loss was 11 pounds, all from fat.

Again though, after tightly controlling all of the variables that could be controlled (eating, exercise, etc), weight loss ranged from less than 5 pounds to over 17 pounds lost.  This was also a 3-month study, so imagine working out twice per day, to a tune of a 1,000 calories per day, and losing less than 2 pounds per month.  This is what happened with some individuals.  On the other hand, some people lost more than a pound per week, during that same time.

Thus far the research has shown that neither a standard diet nor exercise program, where all of the variables were controlled, worked equally well for all people.  In other words, we’re all a bit unique when it comes to both gaining and losing weight.

Bodyweight Set Point

Next up is research into our body weight set point.  What if I made you eat 50% more calories than you needed, every day for 6 weeks?  How much weight would you gain and if I did this with 10 people, what would the variation be between total weight gain? In the early 90’s researchers did just that.  They had 10 people (7 lean individuals and 3 overweight individuals) eat 50% more calories than they needed for 43 days.   During those 6 weeks, weight gain ranged from 11 pounds to 23 pounds, showing again, that we are all a bit unique when it comes to weight gain.

The interesting part of the study though, occurred after those initial 6 weeks, when the participants went back to their “free-living” environments (in other words, they went home and ate regularly).  During the following 5 weeks people naturally started to eat less and lost an average of 55% of their total weight gain.  After week 5 though, almost all of the “automatic” weight loss stopped.

Again though, there was huge variability with some people losing a little over 40% of their weight gain, while others lost 80% of their weight gain.  In other words, some people basically went back to their starting weight after 5 weeks of eating at home while others kept more than 50% of the weight they had gained in the previous 6 weeks.

To highlight the extremes, some people after 3 months (6 weeks of over-eating and 6 weeks of regular eating) weighed 3 pounds heavier, whereas some people weighed over 12 pounds heavier.  This is like one person going on a binge throughout the holidays and ending up 20 pounds heavier and losing only 8 pounds in the next month or so.  Contrast this to someone else who did the same thing, ending up at their starting weight.

oh no baby 200x300 Genetics, Weight Gain and Weight Loss

If this is you right now, don’t despair

This type of studies highlights the “set point” theory of weight.  In other words, we all have a natural “range” that our body strives to maintain.  Within that range, we can eat a bit more food one day, and a little less the next, but our body does its best to maintain that range.  It keeps us within that “bodyweight range” by doing some things such as increasing our metabolism, increasing heat production, increasing fidgeting, and decreasing our appetite…but it’s not perfect.

Some people’s bodies are really good at maintaining that set point, both up and down, whereas others don’t’ have such tight regulation.  In fact, over time, our set points tend to go up, but rarely go back down, as highlighted in this last study.

Are You Doomed? 

So then the question becomes, what happens if you are looking to lose weight and keep it off for good?  Are you doomed to constantly gain weight and struggle to keep it off?  Not exactly and that’s what the next two week’s “lessons” will discuss.  Next week will discuss the factors that you need to consider when you’re eating and the second week will delve into The Seven Principles to Permanent Weight Loss.  Until then, if you have any questions or comments, please feel free to let me know.


  1. Bouchard C, et al (1990) The response to long-term overfeeding in identical twins. N Engl J Med322(21):1477–82.
  2. Bouchard C, et al (1994) The response to exercise with constant energy intake in identical twins. Obes Res 2(5):400–10.  Hat tip: Scott Stevenson:


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