The science behind weight gain and how to use it to your advantage.

Why Do We Gain Weight?

People want to lose weight, but they struggle to do so. That's why weight loss is the number one New Year’s resolution.

Why is weight loss so hard? The first step is to understand why we gain weight.

The medical community, media, and health experts have been telling us for years that the way to lose weight is to eat less and exercise more. This method works on the premise that all the calories we eat are essentially the same. If you eat more calories than you burn in a day you will gain weight. If you exercise and diet, and burn more calories than you consume, you will lose weight. It sounds simple right?

If losing weight really worked in this way, would 1/3 of Americans be overweight? Most people dieting initially get some results, but often gain the weight back within a year. Fortunately, in the field of obesity medicine, the pendulum is starting to swing towards a new approach to maintaining a healthy weight.

A Crash Course In What Causes Weight Gain

Here is the current science on weight gain–it is caused by a hormonal imbalance. Hormones are molecules that deliver messages to target cells within our bodies. Virtually every bodily function is controlled by hormones. Weight gain is to a large degree an effect of the hormone insulin.

What Does Insulin Do?

Insulin is a storage hormone. It is the key that unlocks fat cells and tells them to store any extra glucose in the bloodstream. When your insulin levels are high, your body is in storage mode. The fat cells actively remove glucose from the bloodstream and store it as fat. The key to maintaining a healthy weight is, therefore, to understand how to balance the body’s storage mode with a fat burning mode.

Food is made up of three macronutrients:

  1. Carbohydrates (sugar, bread, pasta, etc)
  2. Protein (meat, egg whites)
  3. Fat

All food stimulates insulin to some degree, however the amount of insulin stimulation varies greatly depending on the type of food. The chart below shows that carbohydrates cause your insulin levels to elevate the most. Protein causes a modest elevation of insulin, and fat consumption results in a very minimal rise in insulin levels.

Effect of carbohydrates, protein, and fat on insulin levels

This demonstrates that all calories are not created equal. When your insulin levels are high, you are actively storing fat, resulting in weight gain. Our traditional teaching of eating a low fat, high carbohydrate diet has resulted in overall weight gain over time.

What Happens When You Eat A Meal?

After you eat a meal, especially one high in carbohydrates, you have glucose circulating in your bloodstream. Insulin levels rise, and the body starts to take action to get the glucose out of the bloodstream. Glucose is first stored in the liver as glycogen. The liver has limited storage space and cannot hold much glucose. If insulin levels remain elevated, the fat cells start storing the glucose as fat.

After several hours, the glucose is removed from the bloodstream, and insulin levels start to fall. This happens every night while you're sleeping.

The body needs a baseline level of glucose in the bloodstream at all times to power the cells of the body, especially the brain. At first, the liver uses its glycogen to keep your blood sugar at the level needed for basic body functions. Once that starts to be used up, the body will access its fat stores and turn fat into glucose, essentially burning fat for fuel.

Podcast Episode: How To Optimize Your Health With Dr Scott Sherr

Why Is Obesity Becoming An Epidemic?

Why is it that obesity has become an epidemic over the past 50 years? The answer lies in both the timing of meals as well as the types of food we are eating.

If you think back to early America, where many people were farmers, they generally ate only three meals per day. They typically went to bed earlier and did not eat late night snacks. Their foods consisted of eggs, meat, and vegetables–with far less sugar and highly refined carbohydrates. Their insulin levels likely looked like this:

Contrast this with the average American today. Many Americans start their day with a carbohydrate-filled breakfast such as cereal, yogurt, pastry, bagels, or something that comes in a wrapper. We eat a mid-morning snack, lunch, a mid-afternoon snack (or two!), and dinner. Many people today stay up late and eat a late snack, dessert, or have a beer while watching late night TV. This is followed by getting up at six in the morning the next day to have breakfast. Many Americans have insulin levels that look like the following:

Notice how most Americans spend all day in Fat Storage mode?

As you can see, our insulin levels are always up, except for a short time while we're sleeping. This means we're constantly in storage mode, and over time our weight will slowly creep up.

How Can We Use This Information?

Looking at how insulin acts as a hormone in the body, we realize that if we control our insulin levels, we can control our rate of fat storage and fat loss. This is a function of the timing of eating as much as it is about the actual food we're eating.

To get started, I have my patients start keeping a food journal. Many people use apps to do this, but honestly, I feel that they're too complicated and time-consuming. Do not count calories–as we just discussed, not all calories are created equal, so counting them is of limited benefit. Just go into your notes on your phone and list what you ate for the day. Here is an example of a simple journal:

  • 7am: yogurt, granola, grande caramel macchiato
  • 10am: apple
  • [12:30]: boxed sandwich with chips, soda
  • 2pm: Soda
  • 3:30pm: trail mix
  • 5pm: cookie
  • 6:30pm: spaghetti dinner, wine
  • 8pm: ice cream

Focus on the timing of when you're eating, and what types of foods you're eating. This includes any beverages other than water, tea, or black coffee. Most importantly, note how often you're eating, and how much time you're giving your body without any food or sugary sodas.

To get started, keep this simple food journal for a week to establish a baseline.

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18 thoughts on “Why Do We Gain Weight?”

  1. I think calories are very important. Even if you eat “good” foods at the “right” time, but just too damn much of it, you’re still going to gain weight. It’s like money – I don’t care if you give me one’s or twenty’s or even write me a check – as long as you pay me! If you are old enough (50’s) you remember back to a time before they had Big Macs and Quarter Pounders. Young people now are incredulous that hamburgers used to have only one patty. (That’s why Big Macs were such a big deal back then as they had not one, but **TWO** patties). Now every adult burger has 2 patties and you have to ask for a “junior” burger if you want just one. A McDonalds Happy Meal clocks in at over 600 calories. And we wonder why are kids are getting heavier.

    • Regarding the small frequent meals, if you look at the graphs of your insulin response, this tells the story of why the small frequent meals do not help with weight loss. You will essentially be in “fat storage” mode all day, with frequent insulin spikes. Also, if you have ever tried the small frequent meals – you never feel satisfied or full – just sort of empty and still hungry. The goal is for this to be easy to maintain a healthy weight, where you feel satisfied. My next post will actually deal with timing of meals, and why it is important. Thank you for reading!

  2. Great article! Really looking forward to your future posts. With the FI community being primarily “numbers” based, the graphs you posted are very helpful. It makes the solution seem very obvious (don’t eat foods that spike your insulin and don’t constantly spike your insulin by eating continously).

    I went on a weightloss journey and was able to shed 75 pounds in a year and a half by following a higher fat/low carb diet and practicing intermittent fasting (skipping breakfast). Looking at your graphs above, it makes complete sense why that worked for me.

    It would be interesting to use an app or website to log what foods you eat and at what times and have the app spit out a graph showing where your insulin levels are at.

    Will you be talking about other hormones as well? In particular, Cortisol?

    • Wow! What an accomplishment. Congratulations on your success! What you described as your method is essentially exactly what the current science supports. I plan to build on these concepts as we go along, and eventually after building the baseline understanding, I will discuss the concept of fasting – who should try it, who should not try it, and what the benefits are. I would be happy to cover cortisol in the future, as you are correct – it does play a role. First the basics!

  3. So interesting! Its so crazy that the science has changed so much. I know that the keto diet has been big right now because of this science although I think it can be hard to follow. I’d love to hear about moderation (e.g., higher fat, lower carbs, moderate protein but still begin able to eat a good amount of veggies and fruit). I tried the keto diet and is seemed so strict that I gave up after weeks. I’m also interested in the timing of meals for athletes. I know that might not be relevant to a lot of FI people but I’ve always been taught the eat carbs right before and right after a workout to replenish glycogen stores. Look forward to reading more!

  4. Thanks for spending the time to write in detail yet plain English the science behind weight loss.
    It ties into a Quora answer I wrote recently about why Italians aren’t fat even though they eat a lot of delicious food (that can be quite carb heavy).

    One big reason is simply that Americans snack more than any other groups of people I know. Americans don’t necessarily eat bigger meals. Yes, you have the odd person who is eating huge quantities of food that you probably can bring up to contradict me.

    But seriously, Americans are snacking so frequently. When I was studying in France, one of my art history professors referred to some students who were constantly eating as “rabbits”.

    “You are always eating like rabbits. Too much snacking. You are even eating in the Louvre!” He found that highly inappropriate, it was kind of funny.


    I also remember a nutrition class I took taught by a Chemistry PhD. He taught the student athletes all kinds of advice like don’t drink chocolate milk after workouts because the sugar content is so high that it is actually counterproductive. Eat a bit of butter if you have amenorrhea. He discovered that from working with Olympic athletes who had extremely low body fat and wanted to get pregnant. etc. etc.

    His information absolutely blew my mind. It contributed to me losing my 25-30 pounds of college weight gain.

    I was sad to learn that the class I attended was the last one he will teach at this university-not-to-be-named because they were firing him from that particular class based on complaints from the athletic coaches. They complained their student were contradicting their nutritional advice and not eating the diet plans they were provided.

    Luckily I recorded as many lectures as I could on my tape recorder. Still need to find time to go through them to pick up extra tips.
    Snacking throughout the day is a problem for my husband. He gets HANGRY if his blood sugar dips. He tells me he has to have snacks or he can’t function. I have witnessed this to be true. He has trouble driving and goes kind of catatonic. Do you have any recommendations for how we can wean him off snacks? Or will some people simply require snacks to be functional? He is not overweight.

    • Anna,
      Thank you for this! Regarding your husband, he should try eating less carbs with his meals, and add in more fat. I will cover satiety in a future post for you – but the quick answer is that he needs some fat so he will feel full and not have a blood sugar dip later. If he eats a meal heavy with carbs (no matter what weight he is), you cause an insulin spike. The more carbs (this includes not only sugar, but bread, rice, pasta, etc) you eat the higher the spike, which is followed by your blood sugar dropping 1-2 hrs later. This results in being HANGRY! In order to stop the swings in blood sugar, he needs to eat less carbohydrates. Stick with this series and we will cover everything you need to know.

    • The diet that you provided the link to here states that it is based on the following:
      “This eating plan includes lots of plant foods in their whole, unprocessed
      form, such as vegetables, fruits, beans, lentils, seeds, whole grains, and
      small amounts of unprocessed plant fats. It does not include animal
      products, such as meat, poultry, fish, dairy, and eggs. It also does not
      include processed foods, including oil and sweets.”

      If you follow this diet you will be doing better than most Americans! It cuts out sweets and processed foods which are terrible for your health. The carbs in many plants are much better than those in processed sweets. It is not exactly the diet that I recommend following, as it is not very high in healthy fats, but it is much healthier than most American’s diets. I personally am not a vegetarian, but a healthy diet does not need to include animal products.

  5. I have lost 10 pounds exercising and avoiding snacks. I weigh 213 at the moment and am trying to get below 200. I am experimenting with fasts. I don’t eat on Thursdays. I also stopped eating lunches. Would it be more efficacious to skip breakfast instead?

    • Christopher,
      Congratulations on your success so far! Avoiding snacks is the way to start. Next start keeping a food log so you can really see what types of foods you are eating and when. There is a role for fasting for some people, and I do plan to cover this in future posts. However, that is an advanced technique, and in general you should make sure you have become a “fat burner” rather than a “sugar burner” first, or fasting will be quite hard. Before fasting, make sure you have cut out the majority of highly processed sugars including soft drinks, sugars, bread, and pasta. This will help you increase your success. Fasting is a big topic, too much for a quick response, but please keep reading!

  6. I am really looking forward to your future posts! This is an area that has crept up a bit in my life. When I was a younger athlete I didn’t have to worry about my weight. Now, even though I am active, I am not where I would like to be.

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