Dietary fibre meets a somewhat different fate. Most fibre resists the digestive enzymes of the intestine and passes through to the large bowel. Here, some of it is metabolised by bacteria that produce the specific enzymes necessary for breakdown. This process is known as ‘colonic fermentation’. The end products include the gases carbon dioxide, methane and hydrogen along with volatile fatty acids called short chain fatty acids (SCFAs). The SCFAs are absorbed from the large bowel, enter the bloodstream and are transported to the liver. The degree of fermentation in the large bowel depends on the type of fibre and varies between individuals. This explains why some people produce a lot of gas and others produce very little following consumption of fibre-rich foods. Soluble fibres are entirely digested by bacteria and produce most of the SCFAs. Insoluble fibres are digested to only a small degree and the amount depends on the time spent in the large bowel before excretion.

The term resistant starch is a relatively new addition to the fibre scene. This is used to describe polysaccharides which are resistant to normal enzymatic digestion. This means that a portion of the starch eaten in foods will pass through the stomach and small intestine to the large bowel where it is fermented in a similar way to fibre. For this reason most nutritionists currently regard resistant starch as a component of dietary fibre. Resistant starch can occur naturally, such as in raw potato or bananas, be formed in partly milled grains and seeds, or can form following heating and cooling of cooked potatoes, bread and cornflakes. The approximate resistant starch content of specific foods. Food manufacturers have been able to incorporate resistant starch into white bread and other foods without affecting the sensory qualities of texture and flavour. This is a major advantage as consumers can eat foods that are higher in this fibre-like substance, but not radically different from more accepted forms.

This new dimension in carbohydrate physiology has stimulated another broad classification of carbohydrates. Nutritional scientists now use the terms ‘available’ (sugars and most starches) and ‘unavailable’ (resistant starch and fibre) when referring to the nutritional implications of carbohydrates.

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Without the presence of a neurotransmitter, an electrical impulse comes to a biological dead end-its message can’t get through. Too much or too little of a given chemical can also affect the rate and the clarity with which the signal is carried. That’s why we speak of chemical imbalance as the cause of a number of mental and physical disorders.

Sitting within the skull, the brain is enmeshed in an intricate network of blood vessels. Before blood can reach the brain, it must pass through a kind of filter known as the blood-brain barrier. This barrier acts, quite literally, as a bodyguard, preventing potentially harmful molecules carried in the blood from gaining access to the brain. For example, the blood-brain barrier will not permit certain drugs to enter the brain and wreak biological havoc.

Blood contains the red cells, which transport vital supplies of oxygen to nourish the brain cells and keep them functioning, and the white cells of the immune system, responsible for protecting the body from invaders. These cells are suspended in plasma, the fluid portion of blood made up of water, minerals, glucose, fats, proteins, and other substances.

The exact composition of plasma is determined in part by the types and amounts of food you eat. Following a meal, the chemical makeup of plasma changes. For example, if you’ve eaten a large steak, the presence of certain amino acids-the building blocks of protein-may increase. When blood containing this particular plasma mix reaches the blood-brain barrier, the different amino acids compete with each other to squeeze through the openings in the filter. Like shoppers clawing their way to reach a K-mart blue light special, only a few can get through.

Different chemical mixtures trigger the manufacture of different neurotransmitters. Let me give you an example. (Bear in mind, however, that not all the facts are in on this intricate process.)

Eating carbohydrates stimulates the pancreas to release insulin, in turn lowering the blood levels of most amino acids. The amino acid tryptophan is unaffected by this process. More tryptophan enters the brain, since there is less competition at the blood-brain barrier from other amino acids. In the next step of the process, tryptophan is converted to a powerful neurotransmitter called serotonin. The higher the tryptophan level, the more serotonin the body can make.

Serotonin circulates in the blood, eventually reaching a certain part of the hypothalamus. When the serotonin level is high enough, it triggers a message that speeds to the other parts of the brain. The message reads something like: “Stop eating carbohydrates now and look for food with other nutrients.” Thus it may be that the specific foods you have already eaten may lead to cravings for other types of foods.

Experiments have shown just how powerful these neurotransmitters can be. For example, animals who normally eat a balanced diet will turn into voracious carbohydrate-cravers, even to the point of endangering their health, if their brains are flooded with certain chemicals that stimulate carbohydrate ingestion.

There are actually three main groups of neurotransmitters involved in the regulation of appetite: the monoamines (of which serotonin is one), the amino acids, and the neuropeptides.

At this point let me introduce the term macronutrients, a word that refers to the major components in food. The three types of macronutrients are carbohydrates, proteins, and fats. Each of these supplies a different type of energy to the body. A balanced diet contains a healthy mix of all three macronutrients. As a rule, animals and most humans will seek out foods that, over the course of time (say, a day) will supply the macronutrient blend their bodies need.

Macronutrients affect the production and release of neurotransmitters. As we saw in the above example, carbohydrate consumption may lead to increased serotonin levels. Similarly, sweet or fatty foods lead to production of certain neuropeptides.

Like a biological traffic cop, the hypothalamus directs all this activity, and it’s a particularly busy intersection. Signals coming from the brain affect the diet, while diet in turn affects the signals heading for the brain. Should something go wrong, a neurotransmitter disturbance might trigger an abnormal pattern of eating. This in turn might worsen the already existing neurotransmitter disturbance, causing more abnormal eating, and so on.

Such findings underscore how chemical messengers spark specific behavior. Controlling the balance of these chemicals through medications might ultimately enable us to bring abnormal eating patterns under control.

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Kirie, a 48-year-old freelance writer from Brinnon, Washington, prided herself on leading a healthy lifestyle. Her diet consisted primarily of grains and vegetables—little meat, little sugar, no junk food. And she walked for a half-hour to an hour every day.

So when the scale showed that her weight had crept up to 159 pounds, Kirie could come up with only one explanation. “Almost every day for 6 years, my job had me sitting for 8 to 9 hours at a stretch,” she says. “Even though I was eating well and exercising regularly, most of the time I was glued to a chair.”

Kirie became convinced that if she could reclaim some of the nervous energy that she had as a child, she could burn a few more calories over the course of a day. So she found ways to incorporate playful, childlike movements into her life. Every morning, she woke with a big stretch. She swung her arms vigorously when she walked. “I’d act childish in the privacy of my home office,” she says. “I’d set a

timer to go off every hour. That was my cue to get up and move. For 15 minutes, I’d squat, skip, wiggle, dance, whatever I felt like doing.”

One year after she began incorporating childlike movements into her daily routine, Kirie went shopping for clothes with her daughter. “I was comfortable with my wardrobe of baggy clothes, but my daughter persuaded me to try on a pair of jeans, something that I don’t usually wear,” Kirie recalls. “I figured that I’d need a size 12 or 14. My daughter looked at me and said, ‘I don’t think you realize how much weight you’ve lost!’

Her daughter was right. Kirie had taken off 40 pounds—and slimmed down to a size 6—simply by acting like a kid again.

WINNING ACTION

Fidget, stretch, squirm. As it turns out, Kirie is on to something. That something is known as non-exercise thermogenesis, which, in plain English, means that you can burn calories without actually working out. A study at the Mayo Clinic in Rochester, Minnesota, found that folks who fidgeted, changed posture, or otherwise moved around a lot during the normal activities of daily living burned many more calories than those who didn’t. As a result, the fidgeters were able to eat more without gaining weight. So go ahead and fidget!

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