The Truth about Carbohydrates

After water, the world eats more carbohydrate than anything else. And our choice of carbohydrate foods and how we eat them has a huge impact on our health, affecting energy levels, mood, weight and sleep in the short term and affecting our risk of heart disease, cancer, Alzheimer’s, macular degeneration , the rate at which we age!  Yet how many of really understand carbohydrates…. For example, clients may tell me “I’ve been avoiding carbohydrates to manage my weight”, then go on to tell me how much fruit and vegetables they eat. They generally mean that grains and potatoes have been off the menu. But carbohydrates are a huge food group:  fruit, starchy vegetables, pulses and grains are rich in carbohydrate. Dairy foods contain a carbohydrate called lactose.  Most vegetables which grow above the ground provide carbohydrate too, but much less of it.  (Exceptionally, pumpkin, squash, sweetcorn and peas are carbohydrate-rich.)

The basic building block of carbohydrate is the simple sugar or monosaccharide – glucose is a monosaccharide. This simplest of carbohydrate provides essential fuel for the brain, red blood cells, the growing foetus; and it supplies the main source of energy for muscles during strenuous exercise. If 2 monosaccharides are joined together they become a disaccharide. Ordinary sugar and lactose, the sugar in milk are both disaccharides. The longer the saccharide chain the less sweet is the carbohydrate. Maltodextrins are oligo saccharides  (oligo meaning a few) are only slightly sweet. Starches are long chains of carbohydrates – polysaccharides – and not sweet at all.

Dietary fibres are big carbohydrate molecules made up of many sorts of monosaccharides. Unlike starches and sugars, our digestive enzymes can’t break them down, so they arrive in the large intestine unchanged. Bacteria begin to ferment and break them down. Different fibres have specific characteristics.  Soluble fibres can be dissolved in water, and some can become very viscous slowing the speed of digestion. Others like cellulose are insoluble and don’t affect the rate of digestion.

Carbohydrate comes mainly from plant foods, and in their unrefined state they usually provide a package of nutrients: vitamins, minerals, antioxidants …  Undigestible fibre has an important role in keeping the gut healthy. But what is the purpose of  digestible  carbohydrate itself?

Carbohydrates have a special role in human nutrition as an energy source. The body runs on fuel derived from a mixture of the protein, fat, carbohydrate and alcohol we consume, and health and energy require the right amount and kinds of fuel. The proportions in the fuel mix will vary on an hourly basis determined by what we’ve eaten. There’s a hierarchy of fuels:  alcohol will always be burned first because it is quickly available and the body has nowhere to store it. But normally the fuel mix will be a combination of carbohydrate and fat in varying proportions. After meals the mix is mostly carbohydrate, between meals mostly fat. The carbohydrate content of food we eat affects the amount of insulin released. The proportions in the fuel of fat to carbohydrate are dictated by the prevailing levels of insulin in the blood. When insulin levels are low, such as when we wake up in the morning, the fuel mix is mostly fat. But eat a high carbohydrate meal and the fuel mix is predominantly carbohydrate.

The significance of our carbohydrate choices for health lies in their impact on the amount and frequency of insulin in the blood, and their effect on the fuel mix our bodies burn.  For example, the body’s ability to burn fat is vital for weight management. Inhibit fat-burning, and fat stores will accumulate. And this is exactly what happens in someone whose fuel mix is predominantly carbohydrate.  Not only are the fat stores not being burned as fuel, but excess carbohydrate (which would otherwise leave too much sugar in the blood) is converted to fat by insulin and stored in the fat cells. We differ in our response to carbohydrate:  genetics, activity levels, and the amount of fat we already have, all have an effect. In one UK study, a group of women were studied for the ease with which their bodies turned carbohydrates into fat. Lean women didn’t make this conversion particularly easily. Overweight women turned carbohydrate into fat twice as easily, and very overweight women three times as easily. So the more fat one has, the easier it is to gain more from carbohydrates.

The health impact of our carbohydrate choices go far beyond weight management. The list includes skin health, energy levels, mood, risk of cardiovascular disease, cancer, macular degeneration, Alzheimer’s, Type II diabetes, the rate at which we age. Insulin is a hormone needed for carbohydrate metabolism, but it has a profound impact on many diseases. General advice to manage the effects of carbohydrate is to eat regular modest meals including breakfast;  avoid sugar and refined foods and go easy on stimulants (tea, coffee, alcohol etc); and aim for a balance every  time you eat. This means including some leaner protein, some good fat (olive oil, nuts and seeds, avocado, oily fish) and a limited amount of a lower Glycaemic Index  carbohydrate-rich food.

The Glycaemic Index (GI) compares how quickly carbohydrate-rich foods are absorbed.  But the GI does not take into account portion size. A more useful measure, which combines the GI of a food and portion size, is the Glycaemic Load or GL. So control the portion size of your carbohydrate rich foods and choose wisely. Most pulses are a good choice with a moderate impact. Starchy vegetables mostly have a moderate effect, but white potatoes and baked potatoes in particular have a very high GI. More moderate GI fruits include berries, apples, pears, grapefruit, plums. Grains can have a high GI: avoiding over-processed breakfast cereals is a good idea, and there is some evidence that some individuals do better with less grain in the diet.

For some people, though, at some times, a fuel mix high in carbohydrates is desirable. Carbohydrate choice produces a rise in blood glucose which affects the insulin response, and that will affect the fuel mix and carbohydrate stores available to exercising muscle. For sports that require high levels of sustained strenuous exercise over 90 minutes carbohydrate choice significantly affects performance:  running or swimming marathons, triathlons, prolonged competitive tennis, rugby or football (depending on player’s position), cross country skiing, lengthy strenuous aerobics or gym workouts. About two hours before an event, eat low GI foods. (Foods that are high in undigestible sugars and fibre can cause gut symptoms in people who are unused to them, so pasta, noodles or oats might be a better choice).  By the time of the event, the food will have left the stomach, and from the small intestine should be slowly releasing glucose energy into the bloodstream. During the event, after the event and after normal training sessions is the time for all the high GI foods that are normally off the menu.  Because high GI foods are absorbed faster and stimulate more insulin, glucose gets back into the muscles more quickly for immediate or future use. During the event, liquids are often better tolerated. A mix of sugars has been found to work well, and mixing a sports drink with some fruit juice is good way to achieve this. If you can eat something solid (perhaps during a cycle race) high-glucose sweets like jelly beans would deliver fast fuel to muscles. After an event or a training session, particularly if more training or another event is imminent, high glucose food are particularly valuable in the first hour after exercise, when muscle is more sensitive to glucose in the bloodstream. Athletes training intensely need plenty of carbohydrates too, to keep the muscle fuel stores at peak levels.  Anyone training intensely two or three times a day would need two or three times the amount of carbohydrate required by an average adult in order to maximise performance.

One of the best things we can do for our children is help them to eat well. The number of overweight children is escalating with all the accompanying consequences for health. Studies have found that giving children meals with a lower GI significantly reduced the amount of food they ate later. So in one study boys ate twice as much in the afternoon after a high GI breakfast and lunch than after low GI versions. Higher levels of insulin after a high GI meals may promote fat storage and obesity. So a low GI diet (together with exercise) should help children whose weight is an issue.

The unfortunate truth seems to be that, for many of us, our genes are way behind the times. Our DNA was designed for a hunter-gatherer diet, with more protein and less carbohydrate. Back then the main carbohydrate sources were fruit and vegetables not cereals. Wheat, rice and other cereals only appeared 10,000 years ago with the agricultural revolution – a mere blink of an eye in genetic terms.  What’s more when those foods were introduced, preparation methods were more primitive and grains were ground between a couple of stones rather than over-rocessed and refined as they are today. All these factors have had a huge impact on the glycaemic effect and insulin response of our diets. We need to consider the type and amount of carbohydrate we eat more carefully.

Ailsa Higgins

After graduating from the Institute of Optimum Nutrition, she directed their postgraduate seminar programme.  She lectures, writes and runs courses, is senior nutritionist at Champneys, works with private and corporate clients, and is regularly quoted in UK magazines.

www.stoptheclock.co.uk