Weight gain catches many of us off guard. It’s often a gradual process that becomes visible many years after it started. If you’re wondering what are the main reasons for weight gain, when does it happen, and what can you do about it, this series is for you.

Let’s start with the basics. Some of you might think it’s very simple. You gain weight when you take in more calories from food than you burn off. That is true. But both sides of this calorie equation are influenced by a lot of factors! Let’s take a look at the main ones. That will help us better understand why weight gain can be hard to avoid throughout life.

What influences your calorie intake?

How much you eat determines how many calories you take in. The problem is that there are several internal and external factors that directly influence how much you end up eating every day. Some of these might surprise you.

Hunger signals – Your body has an intricate system of hormones that reacts to the food you eat and makes you feel hungry or satiated as a result.
Energy balance – Your body also uses hormones to monitor how much energy you’re storing. If you’re undereating or overeating long-term, it pushes you to correct your intake.
Type of foods you choose – We tend to eat more of some foods (desserts) than other foods (lettuce).
Food availability – We also tend to eat more if there’s food within arm’s reach. We don’t eat as much when we have to make an effort to get food.
Your emotions – Many people eat more when stressed or bored.
Social cues – We eat when people around us are eating. Holidays or celebrations are a great example.
Sleep quality – Poor sleep reduces willpower to eat healthy and, to make things worse, it increases hunger hormones.

So, it’s not as easy as saying you should eat less if you want to keep a healthy weight. But the good news is that there are ways to manage all of these factors. But before we take a look at them, let’s go over the other side of the calorie equation.

What influences how many calories you burn?

We usually think of burning calories only when we exercise. While it’s important to know how many calories you expend while cycling if you want to nail your fuelling plan, there’s more that influences your total daily energy expenditure. The scientific literature describes four different parts.

BMR (basal metabolic rate) – This is typically the largest part of your expenditure. BMR says how many calories your body burns even if you do nothing. It’s influenced by your body composition. Muscles burn more calories than fat even at rest. Apart from changing your body composition, there’s not much you can do about your BMR, it’s determined mostly by genetics.
NEAT (non-exercise activity thermogenesis) – This is typically the second biggest part. Non-exercise activity is everything you do in a day that’s not exercise. It includes things like walking, cooking, gardening, cleaning or fidgeting.
TEF (thermic effect of food) – A smaller part of your total expenditure is made up of the thermic effect of food. This means that your body expends energy on digesting food.
EAT (exercise activity thermogenesis) – And lastly, typically the smallest part of your expenditure is exercise. This is how much you burn while cycling, swimming, cross-country skiing or working out in the gym.

As you can see, it’s not as easy as saying you should exercise more to maintain your weight. Exercise is only the smallest factor in your daily expenditure. But then again, it’s the one we have the most control over.

Now that we understand what influences our intake, it’s time to look at the real reason we are gaining weight. Is it a normal part of ageing? Is it due to genetics or does it depend on your lifestyle?