How to gain weight

This article was written in collaboration with Jenup, a non-profit organisation specialising in the early intervention and prevention of eating disorders and body image issues within young people.

Are you medically underweight?

If you think you might be underweight you should check your Body Mass Index or BMI. Any number less than 18.5 generally means you are underweight – although there can be exceptions, for example if you’re of Chinese or Indian descent you could expect to be slighter. Your doctor (GP) can advise you on this. The good news is, if you are underweight there are loads of healthy ways to gain weight, starting with eating the right foods.

The right food for to gain weight healthily

To put on weight you need to consume more calories than your body is burning off. The Government recommends that women eat about 2000 calories a day and men consume about 2500 per day, so if you want to put on weight you should try to eat more than that. But you shouldn’t just go after anything that increases your calorie intake, there are good ways and not-so-good ways of putting on weight.

You may have heard that foods that are high in fat are bad for you, but it really depends on what type of fat we’re talking about.

Avoid saturated fats

Junk food is highly calorific, but stuffing yourself isn’t the best way to gain weight healthily. Fast food and snacks such as crisps are high in saturated fat, leaving you with greasy skin, lank hair and high cholesterol – which in severe cases can cause strokes and heart attacks.

Unsaturated fats are ideal for putting on weight healthily

On the other hand unsaturated fats, such as oily fish, nuts and seeds, avocados, olive oils and vegetable fats, are powerful sources of energy without the negative effects. If you’re trying to work out how to put on weight healthily, things like peanut butter and fish (maybe not served at the same time) are your secret weapon. They can lower cholesterol and provide you with the essential fatty acids you need.

The healthiest way to gain weight is with a balanced diet

A balanced diet containing all of your main food groups is the healthiest way to put on weight. Ideally every meal should contain some protein and some carbohydrates. Proteins can be found in foods like nuts, fish, dairy products and meats. These food groups will help you build muscle mass, rather than adding body fat. Proteins are essential for growth and repairing the body – about 15% of your daily calories should come from protein.

Carbohydrates are an ideal source of energy for the body as they are the easiest to convert into glucose which the body uses to power itself. Basically, if you eat lots of carbs you are more likely to be consuming more energy than you’re burning off. Pulses, bread, potatoes and rice are all good sources of carbohydrates. Fruits and vegetables also contain carbohydrates, as well as vitamins and minerals, so be sure not to forget to eat them too!

How much to eat to gain weight

One of the best ways to gain weight without eating all the time is to increase your portion sizes. If you are used to eating small portions and eating infrequently, try starting to eat slightly more than you normally would – you will find your appetite beginning to increase over time. But you can’t just be expected to double your food intake – there is a limit to what you can eat. Increase your portion sizes slowly over a period of time. Setting weekly goals might help in achieving this.

Be clever with your calories: every time you cook, think how you can add extra calories without just eating more food. Consider mashing your potatoes with olive oil (which is full of healthy unsaturated fats), drizzle dressing on your salad or make creamy sauces for your fish.

When to eat to gain weight

If you can, try to eat every three hours or so, which means you’ll be eating three main meals a day and three snacks. Evenly pace how often you eat to make sure you get a chance to digest your food.

Make it easy to snack by keeping your fridge and cupboards stocked with easy foods – breakfast cereal with full-fat milk is quick to prepare and can be eaten any time of day. If you’re too busy to eat regularly, try and think of ways to cheat. Cook more food than you need for dinner and save half for lunch the next day or take snacks, like bananas, to eat while you’re out.

Try to eat most of your calories during the day if possible. It’s best not to eat loads of food right before bed, as this will reduce the quality of your sleep.

Exercise for the underweight

For individuals who are underweight or in recovery from an eating disorder, exercise should be approached with caution and care.

Light resistance training (such as bodyweight movements, resistance bands, or low-weight dumbbells) can be beneficial for maintaining muscle and supporting mental well-being. However, high-intensity cardio or excessive exercise is not recommended, as it can further stress the body and hinder nutritional rehabilitation.

It’s essential to work with a fitness professional who is specifically trained in eating disorders, as they will understand the unique physical and psychological needs of recovery.

The goal of movement during this phase should be to support health, not control weight or shape. Always prioritise medical clearance and nutritional stability before resuming or starting any new form of exercise.

Keep your GP informed

Putting on weight can be difficult for some people, but if you commit to eating more over a period of time you will achieve your goal.

If you’re consuming more food and not putting on any weight there might be an underlying medical reason. For example, undiagnosed diabetes or an overactive thyroid can be reasons for weight loss. Also if you’re really struggling to put on weight, there are food supplements your doctor (GP) can prescribe for you that can help increase your daily calorie intake. These include high calorie juice drinks or milkshakes which you drink as an addition to meals, rather than as a replacement. If in doubt, get some medical advice.

Being underweight can be just as bad for you as being overweight, so don’t feel you can’t discuss it with your doctor (GP) – they will be interested and will want to help.