Diet, fats and cholesterol

Part 3b: You can eat too much fruit and veges

In the constant fight against infectious diseases, our bodies have a sophisticated defence mechanism - our immune system. When it is functioning properly, our immune system is far more effective than you might imagine: it can dismantle and rid the body of a transplanted kidney very quickly. It can do the same to invading bacteria and viruses if it is kept in good condition.

A major part of our immunity relies on are a type of leukocyte or white blood cell, which circulate in our blood streams and mop up any bacteria, viruses or other foreign bodies they come across. These cells form 60% to 70% of the white blood cells in our bodies. They are generally much more active than any other blood cell. It can be disastrous to our health, therefore, if their effectiveness is compromised in any way. Of all the factors in our modern world that are working against our immune defences, our diet is the worst, for this is exactly what happens if we eat too much carbohydrate and too much sugar in particular.

By 'sugar' I do not mean just the white, granulated stuff we serve from a bowl on the table. That is sucrose; the term 'sugar' applies also to glucose, fructose (fruit sugar), maltose (grain sugar), lactose (milk sugar) and honey (a mix of glucose, fructose, sucrose and dextrin).

Test results

Forty years ago researchers carried out a series of studies that examined how the sugar we eat weakens the ability of white blood cells to destroy bacteria. The results of the study, tabled below, showed that if a person ate no sugar for 12 hours, each white blood cell could destroy an average of 14 bacteria. As sugar intake was increased, so the numbers of bacteria consumed was lessened until, by the time 24 teaspoons of sugar were consumed (the amount in a medium piece of cheesecake or a milk shake), the white blood cells were so compromised that they could only destroy an average of one bacterium each.[1] The implications of this study are obvious. Eat white sugar and you severely compromise your body's ability to fight infection.

But white granulated sugar is only one form of 'sugar' that we eat. In 1973 another study was performed to check the effects of a range of sugars on our immune system. After an overnight fast and their leukocytic index (LI) had been recorded, subjects were fed 100 grams of a specific carbohydrate - a sugar or starch.[2] The table below shows that all forms of carbohydrate - starch as well as sugars - reduced the white blood cells' effectiveness at destroying bacteria and other micro-organisms (the figures are averages across all subjects).

Consequences

Based on these studies, any person who eats largely carbohydrate-based meals, particularly those containing sugars, and snacks with carbohydrate-based meals spread throughout the day - as the latest advice suggests we should - could lose up to half their immunity to disease for much of the waking day.

It is important to note that the worst sugar was fructose. Fructose is the sugar found in fruit - fruits bred today for sweetness are generally little more than sugared water. So if you want to live a healthy life, free from infection, 'five portions of fruit' may not be such a good idea, even if vegetables are.

Diabetics have impaired leucocytic activity and are already at significantly greater risk from infections. Thus diabetics should be even more careful not to consume a carbohydrate- and particularly a fruit-based diet.

Low cholesterol and the immune system

There is one other point on immunity. That is your cholesterol level. You also compromise your immune system and leave yourself open to disease if your cholesterol is low, as we will see in the next part .

References

1. Kijak E, Foust G, Steinman RR. Relationship of Blood Sugar Level and Leukocytic Phagacytosis. South Calif Dent Assn 1964; 32: 349-351
2. Sanchez A, et al. Role of sugars in human neutrophilic phagocytosis. Am J Clin Nutr 1973; 26: 1180-84.

for more on cholesterol and heart disease, see Cholesterol-and-Health.org.uk