The Science Behind Weight Gain

Weight gain is such a frustrating thing. Most people don’t realise that their weight is getting out of hand as it’s happening. There’s usually a moment of shock as a favourite shirt doesn’t close or someone finally musters up the courage to comment about the way you look. That moment where you can no longer tell yourself that you’re fine and things are under control. 

Gaining weight is not spontaneous. Sorry to break it to you. It involves a series of dominos falling culminating in an unhappy visit to Mr Scales. In fact, gaining weight is actually very scientific, in most cases. Note, that doesn’t say genetic! Scientific!

What causes weight gain?

Weight gain is simply caused by an excess supply of energy that’s consumed relative to energy used up. 

The cells in your body (organs & muscles) are run using two primary fuel sources. Carbohydrates or fats. 

carbohydrates fats weight gain

If you provide your body with an abundance of both fuel sources, your body will use one and store the other. 

Carbohydrates for fuel

Carbohydrates (carbs) are a viable fuel source for the body. They can be considered a “fast burning fuel” because the body does not have a huge amount of storage available for carbohydrates. 

Carbs that are consumed are broken down by the stomach & intestines into sugar (glucose). All carbs eventually end up in the bloodstream as sugar which can be used to keep muscles & organs functioning.

Fat for fuel

Fats are also a viable fuel source for the body. Contrastly, they are a “slow burning fuel” that can keep the cells fueled for a longer period of time. Additionally, our body is so good at storing fats for later use if we consume more than we need. 

Fats enter our stomach as triglycerides and broken down to free fatty acids. They can be stored in adipose tissue and every body uses different locations for their fat storage. When needed, the free fatty acid is released and transported through the bloodstream via cholesterol to be used to fuel muscles and organs.

Why can’t we have both?

Elevated blood sugar is considered toxic by the body. Because our bodies cannot store much glucose, it works hard to get it out of our system as quickly as possible.


Insulin is a hormone that’s released by the pancreas to let all the cells in the body know that there is plenty of sugar available in the blood. Essentially, insulin goes around and knocks on the cell “door” asking the cells if it would please take in some sugar in order to get it out of the blood. 

Insulin release is the biggest cause of weight gain. 

When insulin is released, it blocks the body from releasing fat from storage. The body is so desperate to dump sugar out of the blood that its prevents any fat from getting out and being used.

Insulin enforces sugar is used first, fat second. 


Diabetes occurs when the pancreas becomes exhausted from continually producing insulin. Continued insulin release also leads to insulin resistance by the cells. To continue the metaphor from earlier, the cells stop answering the doorbell because insulin is always there begging to take up all the extra sugar that’s in the blood. 

Impaired insulin production and insulin resistance make it even more difficult to slow or reverse weight gain as we lose one of our best tools for ridding the blood of sugar and allowing the body to use fat for fuel rather than keeping it in storage. 

Diabetes shows that perpetual insulin release causes further problems and difficulty with weight gain. It’s basically a downward spiral and makes the climb exponentially more challenging the more weight and fat we accumulate.

Sugar & Carb Addiction

From our experience, sugar addiction is one of the primary causes of weight gain. Most people understand the harms of excessive sugar, but as mentioned earlier – all carbs eventually turn into sugar. So, carb addiction can also occur for some people and is surprisingly less recognisable as a problem. 

As we said, carbohydrates are a fast burning fuel that’s not stored as readily. As a result, when your body is only trained in using carbohydrates and sugar as it’s primary fuel source, it becomes dependent on a steady influx of carbohydrates.

Most of us have plenty of fat saved for a rainy day, but with food being so accessible, our body becomes addicted to a steady supply of carbs and sugars to keep the cells running. If your cells never experience or train in mobilising fat and using it to fuel the muscles and organs, it tends to panic as soon as blood sugar dips. The brain then panics and sends you cravings and urges to refill the blood with even more sugar. This creates a dangerous loop that’s very similar to other addictive behaviours. Your body yearns for the substance, even when there is no real need for it.

Our controversial opinion is that weight gain & obesity are a sign of sugar and carb addiction.

Other psychological factors

To this point, we have addressed the physical causes of weight gain. Psychology and mental health also play a large role in causing and potentially reversing weight gain. In general, psychological factors can be a little more individual and if you think you have a real problem you should seek individual care to increase your chances at success. Here are a few common psychological factors that contribute to weight gain:


Stress can definitely contribute to weight gain. As a result of stress, an overload of the central nervous system occurs and essentially results in disturbances to the “normal” psychological processes. Sleep is ruined, anxiety ensues, productivity goes out the window and so does rationalising food choices. 

The impact of stress may not be as direct as some of the physical factors listed earlier, but it has a huge effect on the choices we make when the mind is occupied with other things. Self control & decision making are sacrificed leaving us vulnerable to poor eating habits, binge eating, comfort foods and sugar addiction. 

Sometimes stress can’t be avoided. But if you can take measures to reducing your stress levels you might just find the weight loss becomes a whole lot easier.

Loneliness & Depression

Similarly, common factors that compromise our decision making ability and leave us susceptible to poor decisions that lead to weight can occur in the form of loneliness and depression. In a very similar way to stress, our minds are not great at performing optimally and regulating our choices when we are overwhelmed with loneliness or depression. 

Get help!

The practical application here is to seek help if you think that your ability to make good choices and remain in control of your eating is compromised by either of these issues. You might want to stop the poor eating choices and make a lasting difference but often it’ll be very difficult to make any positive changes without first addressing the underlying triggers associated. 

Take Action

If you relate to these issues and would like to make a real change, we are here to help. At Activate Clinic, we understand that weight gain occurs as a result of a (long) series of breakdowns both physically and psychologically. We aim to support you through your incredible transformation by giving you eating guidelines as well as individually tailored exercise programs to help you improve your body’s energy balance.

We see many people who think nothing can be done. But with the right help all these issues can be gradually improved to get your body away from storing fat and end the weight gain once and for all. 

Leave a comment, chat to us using the blue button in the bottom right corner, make an appointment or sign up for our intensive weight loss program

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