Review of 200 Studies Confirms That Every Pound Gained Increases Risk of Many Cancers

A review of over 200 studies has revealed a substantial link between body fat and 11 different types of cancer, prompting calls for further research and tougher efforts to tackle the obesity crisis. 

MRI scan of a morbidly obese 250 pound woman (left) and healthier 120 pound woman (right). The areas of pronounced visceral fat are evident on the obese woman around the abdominal cavity. 

Just a few years ago, the first a causal link was shown in a study published in Cancer Prevention Research detailing how visceral fat is linked to colon cancer.

An excess of visceral fat is classically known as central obesity, the "pot belly" or "beer belly" effect, in which the abdomen protrudes excessively. This body type is also known as "apple shaped," as opposed to "pear shaped," in which fat is deposited on the hips and buttocks. Scientists have come to recognize that body fat, instead of body weight, is the key to evaluating obesity. It's one of the reasons Body Mass Index (BMI) is a very poor indicator of health and Body Composition is far more accurate. Biomarkers such as waist-hip and waist-to-height ratios are also linked to cardiovascular function, systolic and diastolic blood pressure, HDL and total cholesterol as well as well-being.

Whilst studies into the link between obesity and cancer are rife, the quality of analysis has often been weak, say a team of researchers at Imperial College London.

In order to provide finer detail of those at most risk, an umbrella evaluation was carried out on 204 studies into adiposity and its link with 36 forms of cancer.

Of those evaluated, researchers found that strong evidence supports the link with only 11 types of cancer.

These were: oesophageal, multiple myeloma (cancer of white blood cells), cancers of the gastric cardia (stomach), colon, rectum, biliary tract system (bile duct), pancreas, breast, endometrium (uterus), ovary, and kidney.

Statistical analysis was carried out to reveal discrepancies and evidence of bias between studies.

The report concluded that besides the connections they found to be strong, 'Other associations could be genuine but uncertainty remains', and called for further research.

Obesity Risks

The report showed that increases of just several kilograms in body weight can significantly increase the chance of developing cancers.

Risk of postmenopausal breast cancer for example, was shown to increase by 11% for every 5kg (11 pounds) gained. Similarly, the risk of colon cancer in men increases 36% for every 5kg increase in body mass index (BMI).

Maria Kyrgiou, a co-author of the study, told FoodNavigator: “Being overweight or obese causes disruption in many hormonal and metabolic pathways. Excess adiposity has been linked to higher oestrogen levels, higher insulin levels and increased inflammation, all of which can affect cell division and therefore cancer development. Reducing the obesity epidemic by tackling the factors that predispose to it, including eating, drinking and exercise habits to mention few, as early as possible would obviously be of utmost importance."

Obesity is one of the principle health issues worldwide. World Health Organisation data shows that one in three children aged 11 in the European region are overweight or obese.

In the UK, 68% of men and 58% of women are obese. The burden on health, labour and care is thought to cost tens of billions.

The researchers advised that policy makers need to focus on obesity prevention programmes at young ages, as soon as possible.

If You Must Exercise For Your Health, Do It For Visceral Fat

Speaking to a meeting of the American College of Sports Medicine in San Francisco, Cris Slentz said he was surprised at how rapidly fat accumulated deep in the abdomens of patients who did not exercise.

Volunteers who did no exercise had an 8.6 percent increase in visceral fat after eight months, while those who exercised the most lost 8.1 percent of their visceral fat, Slentz said.

"The results of our investigation show that in sedentary overweight adults, who continue to choose a sedentary lifestyle, the detrimental effects are worse and more rapid than we previously thought," Slentz said in a statement.

"We probably should not have been surprised since this simply mirrors the increasingly rapid rise in obesity prevalence seen in the U.S., where at present two out of three adults are overweight or obese."

Women gained fat twice as quickly as the men did, Slentz said.

Exercise takes the fat away quickly, but it has to be pretty vigorous, Slentz and colleagues found.

Doing bursts of hard exercise not only improves cardiovascular fitness but also the body's ability to burn visceral fat, even during low- or moderate-intensity workouts, according to a study published in the Journal of Applied Physiology. Eight women in their early 20s cycled for 10 sets of four minutes of hard riding, followed by two minutes of rest. Over two weeks, they completed seven interval workouts.

After interval training, the amount of fat burned in an hour of continuous moderate cycling increased by 36 percent, said Jason L. Talanian, the lead author of the study and an exercise scientist at the University of Guelph in Ontario. Cardiovascular fitness -- the ability of the heart and lungs to supply oxygen to working muscles -- improved by 13 percent. Results were independent from any type of special dieting or food plans.

It didn't matter how fit the subjects were before. Borderline sedentary subjects and the college athletes had similar increases in fitness and fat burning. "Even when interval training was added on top of other exercise they were doing, they still saw a significant improvement," Mr. Talanian said.

You can choose any form of exercise you like. It can be calisthenics or as simple as walking. The key is to start where you're comfortable and build from there. Here's a routine you can try at home:

• Begin walking for a few minutes at a comfortable pace to warm up.
• Increase the pace and lengthen your strides. Let your body adapt.
• Now step up the pace until you're breathing heavy. Keep up the pace for 2-3 minutes.
• Now recover. Keep track of how long it takes your heart rate to return to normal.
• Once your heart rate drops down, do another set. Do this between 2 and 5 times, depending on how you feel.

Although dietary choices influence visceral fat, researchers have found that vigorous exercise is one of the most effective ways to reduce it.

Gender differences do exist for visceral fat and it's important that scientists begin to recognize this significant finding. Huffman stated
"...there are important gender differences in how adiposity and nutrients interact with the tumor environment." He noted that more studies are needed to definitively uncover the mechanisms behind the causality between visceral fat and cancer, to determine how abdominal obesity and nutrient availability act independently during the stages of tumor promotion and progression, and to determine how other strategies to promote weight loss affect cancer risk.

Mortality and financial trends associated with cancer and heart disease seems to suggest that future efforts should increase social marketing awareness of visceral fat and the associated effects in men and women. Which matters the most in the battle of the bulge? Certainly not subcutaneous fat.

This first appeared in Prevent Disease