Body size and health

Key points about body weight and health

  • Many factors influence body size, eg, medical conditions, medicines, genetics, socio-economic status, age and ethnicity.
  • Obesity is a medical term used to describe excess body weight. Having excess body weight may increase your risk of developing certain health conditions.
  • People in larger bodies face discrimination and weight stigma, which also causes higher stress and poorer health outcomes. 
  • Key health behaviours important in determining your health are: eating 5+ fruit and vegetables per day, regular physical activity, not smoking and limiting alcohol.
  • If you're concerned about your weight or health, see your healthcare provider for support to make positive lifestyle changes. 
Overweight couple training canva 950x690
Print this page

There are a lot of studies that show high body mass index (BMI) is correlated with some health conditions. Your BMI is calculated by dividing your weight in kilograms by your height in metres squared (kg/m2).

Health conditions that often occur at the same time as high BMI include:

However, just because these illnesses can occur in people with a high BMI doesn't mean body size is the cause. 

Body size is just one of the ways a doctor can determine your health. Other ways include blood tests, measuring blood pressure, looking at body composition (how much muscle and fat you have) and looking at eating and exercise behaviours. 

Most experts now believe that the obesity epidemic is caused by our modern lifestyle, which promotes overeating and drinking and limits opportunities for physical activity. 

There are 4 behaviours that have the most impact on your health, regardless of body size:

  • eating 5+ fruit and vegetables per day
  • doing regular physical activity
  • not smoking
  • not drinking too much alcohol.

Put simplistically, excess weight is the result of an energy imbalance. This means too much energy (kilojoules/calories) in the form of food is put into your body and not enough energy is used up through exercise and daily movement. The excess energy is stored by your body as fat.

However, the reasons for your body size are not as simple as energy in, energy out. There are many factors that influence body size, such as medical conditions, medicines, income, genetics, age and ethnicity.

Social factors that are out of your control, such as being surrounded by less healthy food choices when you are out and about, and larger portion sizes, also affect what and how much you eat. Healthy food can be costly and can take time to buy and prepare, which can be difficult with modern lifestyles. Physical activity can also cost money and take up time, which can be difficult, especially for parents and caregivers.

This indicates that factors affecting body size include genes and socio-economic status. Living in more deprived communities may mean it's harder to find or afford healthy food and access free physical activities. 

Image: Canva

Size diversity is when people are genetically designed to have different-sized bodies. People can be many different sizes and still be healthy. 

Weight discrimination is when a person is treated in a negative way because of the size of their body. People who face weight stigma have higher stress, poorer health outcomes and are less likely to seek medical attention.

Many people experience weight-based discrimination within the medical system. If you are denied medical treatment because of the size of your body, ask your medical team what treatment they would offer you if you were thin. You can take a support person to your medical appointments and you can seek a second opinion.

Your doctor will use your BMI and the size of your waist to work our whether you are in the healthy weight range for your gender, height and ethnicityWork out your BMI.

However, we know that total body size doesn’t necessarily impact health. Body composition (the amount of muscle and fat you have) and where the fat is on your body can be more important in determining health.

The size of your waist is an indicator of risk for certain health conditions. A waist circumference of more than 80 cm in women and more than 94 cm in men is associated with an increased risk of type 2 diabetes, hypertension and cardiovascular disease. A waist circumference of more than 88 cm in women and more than 102 cm in men substantially increases this risk.

Many people feel uncomfortable being weighed. When you see your GP or specialist, it's okay to say no to being weighed. If your doctor, nurse or dietitian insists, ask them if it is medically relevant. Sometimes they need to know your weight to help manage a medical condition or to work out how much medicine you need. You can ask to not know what your weight is. 

If you have excess body weight, losing weight may reduce your risk of some potentially serious health problems. Even a small amount of weight loss of 5–10% of your total body weight may produce health benefits, such as improvements in blood pressure, blood cholesterol and blood sugars. 

For example, if you have been diagnosed with prediabetes, even small amounts of weight loss may stop this from progressing to type 2 diabetes. However, improving the health behaviours described above can also improve metabolic factors without necessarily needing to lose weight.

 polycystic ovarian syndrome (PCOS) and infertility, modest weight loss (beginning at 2–5%) may bring improvements in menstrual irregularities and fertility.

There are times in life when it is healthy and normal to gain weight, eg, during pregnancy and menopause. When recovering from illness or certain medical conditions, it can be normal and healthy to gain or regain weight, eg, people newly diagnosed with coeliac disease often gain weight when they begin treatment.

There are times when weight loss is not advisable, such as when you are diagnosed with a serious illness such as cancer or kidney failure or if you have an eating disorder. This is true, regardless of your current body size and weight. If you are losing weight and you are unsure why, check in with your doctor or specialist.

If you are concerned about your weight, talk to your doctor or other healthcare provider. Weight is one part of a very big picture and you can ask to get blood tests and blood pressure tested too, which will help give your doctor an idea of your health status. They will also know whether there are community-based health programmes in your area. 

You can also see a dietitian or registered nutritionist, who is trained in nutrition. They can help work out an approach to improving healthy eating that suits your culture and lifestyle. Doing it as a family is a good way to support each other.  

Work out a plan

The best way to improve your health is to make small, realistic changes to your diet and how physically active you are. If you stick to these changes, over time you will increase your fitness and improve your health. 

We know that diets don’t work and it is healthier to be at a higher weight than to lose and gain weight in a repetitive cycle (called weight cycling). 

  • Write down your goals. Make them realistic. You are more likely to stick to goals that are achievable.
  • Make sure the changes are small steps you can stick to long term, eg, adding one piece of fruit to a snack or adding one extra vegetable to your dinner plate, or halving the amount of sugar added to your tea or coffee.

Choose healthy foods and drinks more often

Enjoy a variety of nutritious foods including:

  • plenty of vegetables and fruit – aim for them to be half the plate at each meal
  • grain foods, mostly wholegrain and those naturally high in fibre
  • some milk and milk products, mostly low- and reduced-fat
  • some legumes*, nuts, seeds, fish and other seafood, eggs or poultry, or red meat with the fat removed. 

* Legumes include lentils, split peas, chickpeas and cooked dried beans (eg, red kidney beans, baked beans). 

Drink plain water instead of sugary drinks and/or alcoholic drinks.

Eat with family/whānau and friends more often.

Be mindful when you are eating – sit down and take time to look, smell and taste your food. Avoid eating in front of distractions, eg watching tv, working or driving. You are more likely to enjoy your food and stop eating when you feel satisfied if you are eating mindfully. 

Be as active as possible 

The key is to start small and build on that. 

  • Sit less and move more. Break up long periods of sitting by getting up and stretching or doing something active.
  • Aim to do at least 2½ hours of moderate or 1¼ hours of vigorous physical activity spread throughout the week.
  • Do muscle-strengthening activities on at least 2 days each week.

Doing some physical activity is better than doing none. It's really important to choose a physical activity that you enjoy – you’re more likely to do it more often. Doing physical activity with whānau or friends can also be a fun way to be more active.

Talk to your doctor or nurse if it’s been a long time since you were active or if you have any health problems. Your doctor or practice nurse can also give you a green prescription – support for getting active and feeling better. Read more about green prescriptions.

Get plenty of sleep

Sleep is important in maintaining a healthy weight. Most adults need 7–9 hours of sleep a night. Read our sleep tips if you need help with getting more sleep.

Hang in there

  • One slip-up is not a reason to give up. 
  • Go back to your goals, and consider whether you need to change anything in your plan to help you stay on track.
  • Get help and support if you need it. 

Kiwi Josh Thomson weighed 165kg and would lock himself in his room for days at a time in an attempt to avoid facing the world. Today he is a transformed man. How did he do it?

Image: Steps for Change(external link)

Having shed 70kgs and gained a truckload of self-belief, Josh then undertook a five-month journey along the Te Araroa trail, walking the length of New Zealand. His goal was to raise awareness of youth obesity and depression, and also funds for Healthify. 

We asked Josh what his top tips were for overcoming obesity and depression. In a nutshell here’s what he told us:

1. Only you can change you – start with the small things

Josh says it took a long time to dawn on him that nobody else was going to “fix” him. Everyone had been telling him he needed to change but it wasn’t until that message finally sunk in that things began to happen. He says start by making small changes. “Don’t stare at Mt Everest – put your shoes on and think about base camp instead. Sit there for a year if you have to, but keep thinking about it.”

2. Sell your car, buy a bike – walk wherever you can, whenever you can

You don’t need the gym to get fit, Josh maintains. He began by doing a routine of leg and arm exercises in his bedroom every day until he felt strong enough to start walking. He used to miss out on doing stuff with friends because he couldn’t keep up with them, but after losing 20kg his knees and his head feel better and he now walks an average of 12km a day.

3. Cut out sugary drinks and alcohol – discover the salad jar

There was a time when Josh’s best friends were Coca-Cola and chocolate. Now he’s ditched those in favour of the salad jar and a diet low in processed food, sugar and alcohol. Not only is that good for his weight, it’s good for his mental health as well. Find out more about the wonders of a salad jar.(external link) 

4. Find someone to talk to – find self-respect

Maybe key to all of this is the fact that Josh found a psychologist to talk to about his inner thoughts and feelings. That person taught Josh about self-love and self-belief.  “No matter who you are, if you can find self-power and love for yourself you can plan [a way forward]. I have gained a level of respect in myself and level of integrity: I don’t want to go back to feeling that other way about myself. Write it in a document, where you are now and where you could be if you stick to your plan. The truth is, it is only you that can push yourself forward.”

5. Try exposure therapy

Josh’s counsellor also told him about “exposure therapy” where he was encouraged to face his fears. Exposure therapy involves facing the things you fear without any danger, to overcome anxiety. For example, Josh sometimes takes a more crowded street which he wouldn’t normally feel comfortable entering. He says it shows him that no matter the intensity of anxiety during the act, that feeling isn’t going to be long lasting and is therefore bearable.

6. Join something – help other people

“I want to walk into a room and when I leave everyone feels better,” Josh says with a smile. He has learnt that giving back and becoming part of something bigger than himself makes him feel good and others feel good, too. He has ties with DOC and Kauri 2000 and is a newly qualified scout leader, which he loves. Connecting with other people is a known way to improve mental health.

7. Learn to budget

When you are depressed and anxious money trouble often rears its heads. Josh says learning to budget has helped him achieve his goals and feel better about himself. “Most of my life I was dismal at saving. But with the Te Araroa goal I have saved more over 6 months than in my entire life!” He has top notch gear for his trip and some cool gadgets to get him through.

8. Don’t listen to negativity – imagine a hopeful scenario

Lastly, Josh says he is no longer interested in what other people think or say about him. And when he feels lonely or down he imagines a brighter future. “It’s like hope dragging you towards the future. It’s always evolving and I put in place techniques like this to stay strong.”

Josh's journey

Josh documented his five-month journey along the Te Araroa trail, walking the entire length of New Zealand.  Find out how he got on, on his Facebook page.(external link)

Healthy eating, active living(external link) HealthEd, NZ, 2020


Healthy Heart Visual Food Guide Poster(external link) Heart Foundation, NZ
Food portions(external link) Heart Foundation, NZ
Eat healthy food and move more every day(external link) HealthEd, NZ, 2019
Healthy eating, active living(external link) HealthEd, NZ, 2020


BMI calculator


  1. Eating and activity guidelines(external link) Health New Zealand | Te Whatu Ora
  2. How and why weight stigma drives the obesity ‘epidemic’ and harms health(external link) BMC Medicine, 2018
  3. Weight discrimination and risk of mortality(external link) Psychological Science, 2015
  4. Healthy lifestyle habits and mortality in overweight and obese individuals(external link) Journal of the American Board of Family Medicine, 2012
  5. Excess deaths associated with underweight, overweight, and obesity(external link) JAMA Network, 2005
  6. Associations of variability in blood pressure, glucose and cholesterol concentrations, and body mass index with mortality and cardiovascular outcomes in the general population(external link) Circulation, 2018
  7. Obesity, BMI, and health – a critical review(external link) Nutrition Today, 2015
  8. Central fatness and risk of all cause mortality – systematic review and dose-response meta-analysis of 72 prospective cohort studies(external link) BMJ, 2020
  9. Weight cycling during growth and beyond as a risk factor for later cardiovascular diseases – the ‘repeated overshoot’ theory(external link) International Journal of Obesity, 2006
  10. Why does dieting predict weight gain in adolescents? Findings from Project EAT-II – a 5-Year longitudinal study(external link) Journal of the American Dietetic Association, 2007
  11. Probability of an obese person attaining normal body weight – cohort study using electronic health records(external link) American Public Health Association, 2015
  12. Weight loss and improvement in comorbidity – differences at 5%, 10%, 15%, and over(external link) Current Obesity Reports, 2017


food portions

Food portions

Heart Foundation, NZ

Need help now?

Healthline logo in supporters block

Need to talk logo

Healthpoint logo

Credits: Healthify editorial team. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Elise Penning, Registered Dietitian, Auckland

Last reviewed:

Page last updated: