To gain weight healthily, eat around 300–500 kcal more than you use each day, through 3 meals and 2–3 snacks that are rich in energy and protein – such as milk, yoghurt, cheese, eggs, nut butters, oily fish, beans and wholegrains. Add strength exercise twice a week. Aim for about 0.25–0.5 kg a week.
Check whether you are underweight
First, check your BMI
A BMI below 18.5 is classed as underweight. If you are over 65, a BMI below about 23, or any unplanned weight loss, is worth discussing with your GP. If you have lost weight without trying, see your GP before trying to gain – there may be a medical cause.
Healthy foods for gaining weight
Energy and protein
- Whole milk, milky drinks and smoothies
- Greek yoghurt, cheese
- Eggs, oily fish, chicken
- Beans, lentils, hummus
Healthy fats
- Nuts and nut butters
- Avocado
- Olive or rapeseed oil drizzled on meals
- Seeds sprinkled on cereal and salads
Starchy foods
- Porridge made with milk
- Wholegrain bread, pasta and rice
- Potatoes with a little butter or cheese
Snacks
- Toast with peanut butter
- Yoghurt with fruit and granola
- Cheese and crackers
- Dried fruit and nuts
The NHS advises avoiding the temptation to gain weight with sugary snacks, cakes and fizzy drinks – they add calories but little nutrition and can raise body fat and blood sugar.
Practical tips
- Eat little and often if you have a small appetite.
- Drink between meals, not just before them.
- Add extra energy to meals: grated cheese, a spoon of oil or butter, milk powder in soups.
- Do strength exercise (weights, resistance bands, body-weight exercises) twice a week.
- Track your weight weekly.
Work out your calorie needs with the daily calorie calculator and add 300–500 kcal.
When to see a GP
See your GP if you have lost weight without trying, feel very tired, have stomach problems, have stopped having periods, or if you are worried about your eating. Beat (beateatingdisorders.org.uk) supports anyone worried about an eating disorder.
Frequently asked questions
How can I gain weight fast but healthily?
Aim for 300 to 500 extra kcal a day from nourishing foods, eat little and often, and add strength training. Gaining 0.25–0.5 kg a week is healthy.
What foods help you gain weight?
Milk, yoghurt, cheese, eggs, nuts, nut butters, oily fish, avocado, beans and wholegrains are good energy- and protein-rich choices.
Is it unhealthy to be underweight?
It can be. Being underweight is linked with weaker immunity, fragile bones, tiredness and fertility problems.
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Medical disclaimer: this guide is general information for adults and is not a diagnosis or medical advice. bmicalculatornhs.net is independent and not affiliated with the NHS. Speak to your GP, pharmacist or another qualified health professional about your own health. Full disclaimer.