Causes of weight gain

For most people, the reason they gain weight is a simple one – they take in more calories than they use up and so put on weight. This often happens gradually over many months or years but as a rule, people who prefer foods that are high in fat or contain a lot of energy (calories) in small portions are more likely to gain weight than those who fill their plates with bulky, low-energy foods. Those who gain weight often eat bigger portion sizes too, which means eating more calories and increasing the chance of obesity.

Obesity doesn't develop overnight. It takes about 3,500 excess calories to gain just 0.5kg and most people do not gain more than1kg to 3kg each year. Our weight fluctuates slightly from day to day and this is normal, but you should always aim to stay about the same weight from week to week.

However, there are other reasons why our weight can increase, some of which you may not have thought about. These include;

Our genes

A tendency for obesity may be the result of genetics. There have been genes  identified that either increase or decrease appetite, and people who gain weight may be less sensitive to their body's signals of fullness than people who have little problem controlling their weight. However, genetic factors do not mean that becoming obese is inevitable – obesity can still be avoided despite genes.

Our habits

Our eating habits develop over many years, and are strongly influenced by our first tastes as babies and the diet that we are given in childhood which can lead to a regular intake of too many calories and weight gain.  Replacing negative eating habits with positive ones is key in weight control. So, if you always eat snacks when watching TV, use healthy alternatives instead such as fruit or vegetables.

Our emotions

Overeating can be triggered by emotions and stress can cause some people to reach for food or alcohol as a way of dealing with this. This can also happen if you are feeling tired, bored or sad.

Medical conditions

Some medical conditions can also cause weight gain. Examples of these include an underactive thyroid gland, polycystic ovary syndrome (PCOS) in women, depression, and heart failure.


Drugs that treat high blood pressure, steroids -  taken for many inflammatory conditions including arthritis, eczema and asthma - and antidepressants and mood stabilizing drugs can all cause weight gain by stimulating the appetite or reducing energy expenditure. If you think this may be a reason for your weight gain, never suddenly stop taking your prescribed medication unless you have spoken with your doctor or specialist about it. In the meantime, make sure you’re following a healthy, balanced diet.

Physical inactivity

People who lead a physically active life are less likely to gain weight than those who spend most of their day sitting in front of a computer or TV, or driving in the car.

Food labelled as 'low-fat'

Lots of foods in supermarkets today are labelled 'low-fat' but in some cases, low-fat foods contain high levels of sugar. High sugar foods can also contain lots of calories, which contribute to weight gain. To avoid this, read the labels and look at the overall energy and calories contained in the food.

Lack of sleep

There seems to be a link between lack of sleep and putting on weight so try to get more sleep whenever possible. If you have trouble sleeping, get advice from your doctor.

Portion sizes

Over the last few decades, the size of portions served in restaurants and supermarket packages has increased. To reduce the effect of this, stop eating when you feel full and eat more slowly. At home, serve yourself a smaller portion and think about whether you really want a second helping. Avoid ‘supersizing’ portions when eating out and whenever possible try to cook fresh, healthy meals at home instead of eating out or buying supermarket ready meals.

Putting on muscle

Sometimes it can be frustrating to find you are putting on weight even when you are exercising hard. Muscle gain is the most common reason for weight gain caused by exercising since muscle is comprised of small dense (and therefore heavy) fibres whereas fat is comprised of larger, less dense droplets. This means that even if you lose fat, you may gain weight if you’re gaining muscle at the same time. However, gaining muscle weight usually comes with developing a smaller waistline, more definition, and a positive change in your physical appearance, all of which are nothing to worry about!!