Weight – tips to gain it

Key points about gaining weight 

  • To gain weight you must eat more kilojoules every day from a range of healthy foods while maintaining regular exercise.
  • Some people are naturally lean and healthy but others are underweight due to an underlying problem or condition.
    People find it hard to understand that being underweight can be unhealthy.
    • Being underweight increases your risk of certain health conditions.
    • You are more likely to die at a younger age.
    • Underweight women have less chance of becoming pregnant than women who are a healthy weight.
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The most widely accepted method to assess weight is body mass index (BMI). It determines whether your weight is putting you at risk and is based on your height and weight. The normal weight BMI range is 18.5 to 24.9. Having a BMI of less than 18.5 indicates that you may be underweight.

Whilst BMI is a useful measurement of weight for most, it is an estimate and is not able to separate between body fat and muscle mass. Active and muscular people may have a higher BMI without being “overweight”. There are also different “normal” ranges of BMI for people of different ethnicities, due to differences in the proportion of body fat. 

Being mildly underweight (BMI of 18) doesn’t necessarily mean serious health problems, but people who are very thin may lack energy reserves, are prone to getting infections and feel the cold because they don’t have a layer of fat to keep them warm.

If you have lost weight without trying to, or don't know why, it's important to see a doctor to check for possible underlying issues. If you have been mildly underweight all of your life and both your parents are too, this is more likely to be ‘normal’ for you and less likely related to an underlying issue. 

For most people, being underweight means poor nutrition – insufficient kilojoules eaten on a regular basis.

Reasons why people might have weight loss include: 

  • depression.
  • stress or anxiety
  • social isolation
  • ongoing (chronic) pain
  • an elderly person who is housebound
  • ongoing (chronic) dieting
  • swallowing disorders
  • gastrointestinal problems eg, coeliac disease
  • chronic illness such as renal disease
  • Alzheimer's and dementia.

To gain weight you must eat more kilojoules every day from a range of healthy foods. Regular exercise is important to help build muscles so that weight gain is not just fat. To gain 1kg of weight in a month requires 1000 extra kilojoules a day.

A plan to increase weight should focus on:

  • Increasing your food intake – try eating larger portions.
  • Increasing the frequency of eating, eg, snack between meals. 
  • Relaxing the rules on how much fat you eat. Fat contains more than twice the kilojoules protein and carbohydrates contain, so increasing your fat intake can rapidly make a difference to weight gain. Add some healthy oils (eg, olive oil, canola oil) to your meals.
  • Including energy dense foods throughout your daily meals, eg, peanut butter or cheese on toast instead of marmite, a milkshake instead of low fat milk, ice cream on fruit, avocado instead of cucumber, juice and milk instead of tea and coffee, Complan or Sustagen drink.
  • Avoiding too many bulky low energy foods. Raw vegetables and fruit are nutritious but you fill up quickly well before you have eaten enough kilojoules.
  • Trying to eat 5–6 smaller meals as this may be easier if bigger portions are difficult to eat.

If you have lost weight due to an illness you may benefit from a liquid nutritional supplement. Dietitians and doctors can recommend these.

Tips to increase kilojoules

  • Eat cereals with added fruits and nuts.
  • Make porridge with milk instead of water.
  • Add jam, cheese, avocado and plenty of margarine spread to toast.
  • Eat cream and ‘mealy’ soups instead of clear soup. Make with milk and top with cheese or croutons.
  • Snack on dried fruit.
  • Add nuts into cereals and baking.
  • Raw vegetables and salads are low in kilojoules but you can add avocado, nuts, sunflower seeds or raisins.
  • Choose desserts that are nutritious as well as high in kilojoules, eg, milk puddings, steamed fruit puddings, custard, ice cream.

Many underweight people can feel uncomfortably full when they start eating larger portions more frequently to gain weight. This feeling does go away eventually, but it takes some perseverance. A major barrier to underweight people gaining weight is their unwillingness to eat more food. Increasing your kilojoule intake is necessary to increase your weight.

Make a tasty drink for one!

Chocolate milkshake Mango smoothie Sustagen
250ml milk 2 Tbsp yoghurt 1 Tbsp skim milk powder 2 Tbsp chocolate topping. Place ingredients into a food processor or blender and process until thick and frothy. Pour into a glass and serve immediately. Kilojoules/serve: 1160 250ml milk 1 Tbsp skim milk powder 1 Tbsp honey 4 ice cubes ½ mango, stoned, peeled and chopped. Place ingredients into a blender or food processor and process until smooth. Pour Into a glass and serve immediately. Kilojoules/serve: 1315 Mix 60g, 3 level Tbsp of Sustagen powder with 200ml milk. Pour into a glass. Kilojoules/serve: 1370

Tbsp = tablespoon

Sample menu

Breakfast Morning tea Lunch Afternoon tea Dinner Supper
  • Porridge with brown sugar and milk.
  • Toast and margarine topped with avocado and tomato.
  • Cup of tea with milk.
  • Berry muffin.
  • Milkshake.
  • Creamy mushroom soup.
  • Cheese on toast.
  • Cake or biscuit.
  • Glass of Complan.
  • Meat, chicken or fish.
  • Scalloped potatoes (with milk and cheese).
  • Small serve vegetables.
  • Sticky date pudding and custard.
  • Milo made with milk.
  • Toasted muffin with margarine or jam.

Eating healthy(external link) Cancer Society New Zealand
Healthy Heart Visual Food Guide Poster(external link) Heart Foundation, NZ
Choose a balance of healthy food every day poster [JPG, 82 KB] Ministry of Health and Health Promotion Agency, NZ, 2020


  1. What to do if you are underweight(external link) Healthdirect, Australia


choose balanced

Choose a balance of healthy food every day poster

Ministry of Health and Health Promotion Agency, NZ, 2020

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Credits: Healthify Editorial Team. Healthify is brought to you by Health Navigator Charitable Trust

Reviewed by: Dr Peter Ou, GP, FRNZCGP, Auckland

Last reviewed:

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