Weight gain

Written by Katherine Nicholls
Katherine Nicholls
Nutritionist Resource Content Team

Last updated 20th January 2022 | Next update due 19th January 2025

Do you want to gain weight? Nutritional therapy can support your weight gain journey in a safe and healthy way, ensuring it is sustainable and realistic in the long term. 

But before you try to put on weight, you need to know that it is safe for you to do so. The best way to do this is to speak to your doctor. They can review your current weight as well as check there are no medical reasons causing or contributing to your low weight.

Once they have an understanding of what is causing your weight loss, your doctor can discuss with you your options. This is where a nutrition professional can help.

How to gain weight

In this video, nutritional therapist Esther Donoff (BSc, MSc) shares some general considerations on how to adapt your diet and lifestyle to help you gain weight healthily.

Want to know more? Read How to gain weight.

Ensuring your diet is balanced and provides enough calories for your height, age and activity levels is key. As tempting as it may be to start eating as much as you can to gain weight quickly, it’s better for your body if you gain weight slowly.

Avoid relying on a diet full of foods that contain lots of sugar and saturated fat. This type of diet is likely to increase body fat and may affect cholesterol levels and overall health. Instead, look to eat a nutritionally balanced diet that contains regular meals and snacks. Current guidelines from the NHS recommend adults aim to eat:

  • at least five portions of fruit and veg every day
  • meals based on starchy carbohydrates like pasta, rice or potatoes
  • some dairy (or dairy alternative), try full-fat milk while trying to gain weight
  • protein such as fish, meat, eggs, pulses and beans
  • two portions of fish a week (one of which should be oily, like salmon)
  • unsaturated oils and spreads in small amounts

They also advise plenty of fluids (six to eight glasses a day) but recommend avoiding just before eating as this can make you feel too full to eat.

Eating a wide variety of foods will help you get the nutrients you need while keeping your palate interested. Try to bring more joy into your mealtimes and celebrate food with social gatherings now and then.

What to eat to gain weight healthily

What foods can you include in your diet to increase and maintain weight?


"Protein-rich foods can be very valuable when you want to improve your body’s strength, immune system and stabilise energy levels and moods," explains Jane Clarke, dietitian and founder of Nourish.

"Often when you’re fighting diseases such as cancer, your body has a tendency to break down your muscles and leave you feeling weak and vulnerable, so it’s a priority to increase your intake of protein-rich foods to help counteract the effects of the disease and treatments."


"Complex carbohydrates including sweet potatoes, porridge oats and wholegrains provide valuable energy and nutrients," says Jane. "They are also processed by the body more slowly than their refined counterparts such as white bread and pasta, and the effect is enhanced if you eat them with some protein such as fish, eggs or nuts."


"Fats provide a great source of calories, but can also make a dish taste better, which can be just what’s needed when you’re struggling with a jaded appetite. Add butter, cream, full-fat Greek-style yoghurt, olive or avocado oil to dishes."

Read the full article on what to eat to gain weight.

We want to make sure that every mouthful you’re having is really nutrient and energy-dense, so we talk about food being energy-dense as they amount to calories in a particular food.

- Esther Donoff

Why am I losing weight?

There are several factors that may lead to someone being underweight. For some, it’s down to family genetics and a naturally slight figure, for others an illness may be the cause. Below are some examples of what can cause a low weight.

  • a high metabolism (those with high metabolisms may struggle to gain weight even when eating high-energy foods)
  • genetic disposition (for some, low weight runs in the family)
  • frequent exercise (those who are very physically active may find they have a low body weight)
  • physical illness (illnesses like diarrhoea may cause you to lose weight temporarily while long-term conditions like diabetes, cancer and digestive issues can lead to ongoing weight management struggles)
  • mental illness (some mental health conditions can affect weight, including depression, anxiety and eating disorders)

If you’re concerned about illness, whether it’s regarding your physical or mental health, visit your doctor for support and treatment advice.

Unintentional weight loss in older adults

Sometimes when we get older we may find we lose weight. This can be due to illness or simply a loss of appetite. Being underweight as an older adult can be especially serious, risking health problems like fragile bones and susceptibility to infection.

If a lack of appetite is affecting your weight, try switching up your portion sizes and eating smaller meals more frequently rather than three big meals. Eating with friends and family can help to increase your motivation to eat too.

If you struggle to prepare food try nutritionally balanced ready meals, keeping tinned and dried fruit and frozen vegetables. You may also want to consider having your meals delivered through ‘meals on wheels’.

Find a nutritionist who can help with weight gain

What are the risks of being very underweight?

In a society that often praises bodies at a low weight, you may think there isn’t a problem with being underweight. The truth, however, is that being very underweight can lead to health problems. Below are a few to be aware of.

Nutritional deficiencies

If you’re underweight, you may not be taking in key nutrients your body needs. If you don’t consume enough iron, for example, you could develop anaemia which makes you feel very low in energy.

Fertility problems

If you menstruate and become very underweight, you could find your period stops. This can lead to difficulties for those trying to conceive.

Weakened immune system

Being underweight can affect the immune system, meaning it won’t work properly. When this happens, the body is less able to fight infections and you may find you pick up viruses and infections more easily.

Skin, hair or teeth problems

If you are deficient in certain nutrients, you may notice your skin, hair and teeth are affected. You may notice dry skin, thinning hair or problems with your dental health.


The food we consume gives us energy. If you’re not eating enough energy-giving foods, you may feel more tired than normal. This can make day-to-day tasks more difficult.


Bone health can be affected if you’re underweight, especially if you aren’t getting enough calcium in your diet. Osteoporosis is a condition that causes bones to be more brittle and prone to breaking. 

Can a nutritionist help me gain weight?

A nutritionist will be able to work with you to create a plan for you to gain weight slowly and healthily. If you have any digestive issues (such as an allergy or intolerance) or a special diet (if you’re vegan for example) they will take all of this into consideration.

Before you meet with them, they may ask you to keep a food diary so they can understand your current eating habits. This will help them see where any gaps may be in terms of calories and nutrition. They may also ask you about your general health, mood and well-being (anything that may contribute to a lack of appetite).

The aim of the nutritionist will be to create an eating plan that you will enjoy and stick to in the long term, making adjustments as necessary once you reach a healthy weight. It’s important, therefore, to be honest with them and let them know if there are any parts of their plan you are struggling with. Together you can make changes to ensure you’re enjoying the food in your plan.

Having regular sessions with a nutritionist will help you stay motivated and offer a sense of accountability. They can also offer gentle encouragement and answer any nutrition-related questions you may have along the way. Having this sort of professional support can be invaluable in finding a sustainable way to gain weight.

Helping you to set tangible goals is another way nutritionists can support you. Often we have a rough idea of our goals, but making it specific and putting a timescale on it can be tricky. This is what a nutritionist can help with, offering an unbiased and realistic view.

- Read more about how a nutritionist can help you attain weight goals.

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