Energy-dense foods and cancer

Various environmental factors increase the risk of cancer, especially smoking and other use of tobacco; some infectious agents; radiation; some medications; some industrial chemicals and pollutants.

It is also known that other environmental factors, such as our diet and physical activity levels, can reduce our risk of cancer. The choices we make about what we eat, drink and how active we are each day will together give us important protection against cancer at all times of life, from childhood to old age. It is therefore clear that cancer is, in large part, a preventable disease.

In previous instalments of this column, I had focused on the importance of body weight and physical activity in reducing risk to various cancers. In several subsequent instalments, I will focus on the role of foods and drinks. I will continue to rely on the World Cancer Research Fund (WCRF) expert report on Food, Nutrition, Physical Activity and the Prevention of Cancer, released in November 2007, to emphasise the importance of the prevention of cancers.

This write-up focuses on the third WCRF recommendation: Limit consumption of energy-dense foods and avoid sugary drinks.

The evidence

The WCRF expert panel found that excessive consumption of energy-dense foods and sugary drinks increase the risk of weight gain, overweight and obesity. This, in turn, increases our risk of a range of cancers, including bowel cancer and breast cancer, especially in postmenopausal women.

It can be difficult to control how much energy you are consuming if you eat a lot of energy-dense foods because you only need to eat a small amount to take in a lot of calories.

On the other hand, foods low in energy density are high in water and dietary fibre. These foods help us feel fuller for a longer time. They are a healthier choice for weight maintenance and probably help us avoid weight gain and obesity.

Where we store the extra weight in the body also affects cancer risk. It is known that excess fat around the waist can be particularly harmful as this may increase risk to bowel cancer.

WCRF recommendations

The recommendation of WCRF is therefore: Limit consumption of energy-dense foods and avoid sugary drinks.

The public health goals, which are for populations and are therefore principally for health professionals, are:

·Average energy density of diets to be lowered towards 125 kcal per 100 g

·Population average consumption of sugary drinks to be halved every 10 years

The personal recommendations, meant for people, as communities, families and individuals, are:

Consume energy-dense foods sparingly
Avoid sugary drinks
Consume “fast foods” sparingly, if at all
This overall recommendation is mainly designed to prevent and to control weight gain, overweight, and obesity.

Energy-dense foods here are defined as those with an energy content of more than about 225–275 kcal per 100 g; the term “fast foods” refers to readily available convenience foods that tend to be energy-dense and consumed frequently and in large portions.

Understanding energy content of foods

Most foods provide us with energy (calories), the amounts expressed as kilocalories or kcal. This energy is utilised by the body to carry out various life-support activities. Energy is therefore essential for life. Excess energy, however, is to be avoided as those not utilised by the body are stored as fat and body weight increases. The long-term effect of excess energy intake is obesity.

Energy in a food is contributed by protein, carbohydrate and fat. These three nutrients in foods, when absorbed into the body, are metabolised (broken down) to provide energy, the most common nutrients being fat and carbohydrate.

Fat is more energy dense because each gram of fat gives 9 kcal when utilised in the body. Each gram of protein and carbohydrate is able to provide 4 kcal of energy when metabolised.

Understanding the amount and energy density of a food and a diet is useful in guiding us in making food choices.

For pre-packaged foods, the amount of energy in each 100g and serving of the food is given on the nutrition information panel (NIP) of the food label. The Malaysian food law requires that the amount of energy and the content of protein, carbohydrate and fat be declared on the label of a wide variety of food products. The food manufacturer arranges for a laboratory to analyse the energy and nutrient content of their food products and have the results declared in the NIP.

The consumer can therefore read the NIPs to understand the calorie content of foods before purchasing such products. You can use the NIPs to compare the calorie content (and other nutrients) of different brands of a similar product.

The energy and nutrient content of many fresh foods and cooked meals have also been analysed in the laboratory of research institutes and universities and made available.

These data are available from the Nutrient Composition of Malaysian Foods, which I published when I was in the Institute for Medical Research. The book contains information on energy and 18 nutrients for 600 raw and processed foods as well as 200 cooked dishes and meals.

The former group of foods includes common daily items such as rice, bread, milk, fruits and vegetables. The latter group includes a variety of popular hawker foods and snacks and franchised fast foods.

A simplified version of the data can be obtained from the “food database” module of the Nutrition Society of Malaysia website (www.nutriweb.org.my).

What are energy-dense foods?

The energy content of foods differ greatly. Some foods contain more energy weight-for-weight than others. Foods that contain high amounts of calories are known as energy-dense foods.

It is not necessary to memorise the energy content of various foods so as to reduce consumption of energy-dense foods. I would not recommend that as it takes the fun out of eating! You just need to understand the ingredients used in the food product and the method of preparation or cooking to estimate the energy density.

Try to reduce intake of foods containing fat and sugars as main ingredients. Also try to reduce consuming too much fried foods as they would generally contain higher amounts of oil.

The WCRF report particularly highlighted that fast foods tend to be energy-dense. They are readily available, and we often eat these foods in big portions too. Excessive consumption of these foods can lead to weight gain and obesity. The WCRF recommendation is to consume fast foods sparingly.

The WCRF report also highlighted that regularly consuming sugary drinks contributes to weight gain. More and more of us are consuming these drinks frequently, and often in “super-sizes” too. They are easy to drink in large quantities but don’t make us feel full, even though they are quite high in calories. Sugary drinks include fizzy or carbonated drinks, cordials and syrups. We should try to avoid these drinks. Water is always the best choice.

Fruit juice counts as one of our recommended five servings a day of vegetables and fruits, but it does contain a lot of sugar, so it is best not to take excessively. You should also try to have pure fruit juices rather than juice drinks which may contain low amounts of fruit.

Eat and drink wisely

The WCRF expert panel has highlighted that choosing healthy foods and drinks instead of those that are high in fat, sugar and calories (energy dense) can help us avoid overweight and obesity and reduce our risk of cancer.

However, it does not mean that we should avoid eating energy-dense foods altogether. The energy density of a food is indeed important, but it is the total amount of energy consumed that is the most important. This depends on how much and how often one eats a particular food. We can therefore certainly consume these foods occasionally, or in small quantities. You can certainly enjoy that higher calorie chocolate occasionally.

You should not make energy-dense foods the basis of your diet. By choosing a diet based on lower energy-dense foods, you can actually eat more food but consume fewer calories. In this way, you will be able to consume a variety of foods.

Also remember, whatever you eat, even for low energy foods, don’t eat till you feel you are full to the throat! It is always wise to remember to eat only up to about 70% full.