Body size and health

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:

• type 2 diabetes
• heart disease
• stroke
• several common cancers
• osteoarthritis
• obstructive sleep apnoea
• reduced fertility.

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. 

What has the biggest impact on your health?

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.

What factors affect body size and impact health?

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 credit: Canva

What is weight discrimination?

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.

How is healthy body weight measured?

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 ethnicity. Work 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. 

When is it good to lose weight?

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.

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

When is it good to gain weight or not to lose it?

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.

What can I do if I am concerned about my weight?

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. 

Learn more

Healthy eating, active living Ministry of Health, NZ

References

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

Information for healthcare providers

Adult weight management Auckland Regional HealthPathways
Clinical guidelines for weight management in NZ adults Ministry of Health, NZ, 2017
Obesity – information for health professionals Ministry of Health, NZ, 2020
Eating and activity guidelines Ministry of Health, NZ, 2018
Addressing weight issues in young people and families in NZ BPAC, NZ, 2012
Weight loss – the options and the evidence BPAC, NZ, 2019
The role of pharmacotherapy in obesity management – introducing liraglutide 3 mg (Saxenda®), Research Review and Goodfellow Symposium, NZ, 2021

Reviewed by

	Elise Penning is a registered dietitian and food and nutrition blogger. Elise specialises in the non-diet approach and works with fussy kids, weight concern in children, disordered eating and binge eating.