Cancer Prevention Tips: Be as lean as possible without becoming underweight

Posted on: 16 Jan 2016

The number one recommendation for cancer risk reduction is to stay as lean as possible within a healthy weight range. This may be one of the most important ways to prevent cancer. Maintaining a healthy weight - through a balanced diet and regular physical activity - helps reduce the risk of developing cancer.

There is strong evidence that weight gain, overweight and obesity increases the risk of a number of cancers. Epidemiological studies have provided convincing evidence that obesity increases the risk of many cancers and that as your weight increases, your risk of developing cancer also increases in a dose-response relationship.

Research has also shown that many types of cancer are more common in people who are overweight or obese, including two of the most common types of cancer – breast and bowel cancers - and three of the hardest to treat – pancreatic, oesophageal and gallbladder cancers.

Almost one person a day is now dying of cancer in Ireland due to being overweight. Another two people are being given a cancer diagnosis every day due to their weight. It’s estimated that overweight and obesity has caused 4,157 cancers in men and 3,682 cancers in women over a decade. Cancer mortality is about 70% higher in people who are extremely obese than in people of normal weight.

How can I find out if I am healthy?

You can find out whether your weight is within the healthy range by working out your body mass index, or BMI. BMI is a useful tool for finding out if you have a healthy weight for your height. But remember, it is only a guide and is not accurate for some groups of people, like pregnant women, children or professional athletes. The associations of BMI with the risk of death show higher risks of death observed in the upper BMI categories. The normal range is 18.5-24.9. It seems the lower end of this range is most beneficial. There are some other studies showing that waist circumference is more strongly related to cancer risk than BMI alone (e.g. colon cancer). A useful indicator of whether you are a healthy weight is to measure your waist. Put the tape measure about an inch above your belly button. The definition of abdominal obesity is >80 cm for women and >90cm men.

Abdominal fat distribution was found to be positively associated with the risk of death in a study of over 350,000 people. When too much fat is carried around the belly, it can do even more damage than fat on other parts of the body. So-called ‘apple’ shape body types are linked to bowel, kidney, oesophageal, pancreatic, breast, and womb cancers. It isn’t clear exactly why this is, but it could be to do with how quickly certain chemicals from fat can get into the blood.

Why do people become overweight or obese?

Simply put, obesity is the result of taking in more calories through your diet than you are burning. The reasons for this calorie imbalance vary from person to person. Most people can reach and stay within a healthy weight range by eating healthily, eating smaller amounts and becoming more active.

Why is being overweight linked to so many different types of cancer?

Fat cells in the body are active and produce hormones and proteins that are released into the bloodstream and carried around the body. It’s essentially a huge gland sending out a constant stream of biological information and instructions that affect the rest of your body. This helps control processes like growth, metabolism and reproductive cycles. Because they are spread through the circulation, these ‘chemical messengers’ can affect many parts of the body. Excess body fat results in an increased release of these hormones and chemical messengers. When the normal levels of these signals are altered, it can increase the risk of several different types of cancer.

What does insulin and oestrogen do?

The hormone insulin is a very important part of how the body uses energy from food. When people are overweight or obese, there is much more insulin present in the body. Higher amounts of insulin can change the levels of growth factors available to cells. Both insulin and these growth factors can become a danger when it comes to cancer as growth factors are a green light signal for cells to divide.

Another hormone released by body fat is oestrogen. One of the strongest links between obesity and cancer is an increased risk of breast and womb cancers in women who are overweight or obese after the menopause, and this relates to higher oestrogen levels. Women who gain > 9kg from 18 years of age to midlife double their risk of breast cancer compared women who maintain stable weight.

What role do macrophages play?

As people become obese, and more fat cells build up in their tissues, specialised immune cells (called macrophages) are called to the scene, possibly to clear up dead and dying fat cells. But as macrophages carry out their clean up job, they also release a potent cocktail of chemicals called cytokines that summon other cells to help them out. The number of macrophages in obese fatty tissue can be substantial – they can account for as many as 4 in 10 cells. This ultimately creates a condition called chronic inflammation – and this is another way that obesity is thought to fuel the development of cancer. And it’s been shown that obese people tend to have higher levels of inflammatory cytokines in their blood. The result of inflammation is a cocktail of signals that tell cells to divide. This is because inflammation usually occurs after injury and after injury you need new cells for healing to occur. This increased cell division can lead to a higher risk of cancer, as cancer occurs when cells rapidly divide.

Why is a healthy body weight as important for for children as adults?

By encouraging your children to lead a healthy lifestyle, you can help them keep a healthy body weight later on in life. A person’s body weight can be influenced by what they ate when they were children, or even what their mothers ate before they were born.

Children who are very heavy at 2 years of age tend to have a higher chance of being overweight later in life. Some studies have found that people who are overweight or obese as children have higher risks of some cancers, obesity, premature death and disability in adulthood. But in addition to increased future risks, obese children experience breathing difficulties, increased risk of fractures, hypertension, early markers of cardiovascular disease, insulin resistance and psychological effects.

Visceral fat is the fat inside your body that surrounds your organs. This fat is more dangerous than the fat you can see. The good news is that visceral fat yields fairly easily to exercise and diet, with benefits ranging from lower blood pressure to more favourable cholesterol levels. It takes a short time for visceral fat to be reduced by simple diet and lifestyle changes. Blood tests show that within half an hour of starting exercise, there are already metabolic changes to visceral fat.

Weight loss also leads to a reduction in inflammatory markers and insulin. There are consistent findings of reductions with weight loss.

Click here to read about how being physically active for at least 30 minutes every day can affect your cancer risk.

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