Deadly Harvest: The Intimate Relationship Between Our Heath and Our Food (22 page)

The results surprised him and surprised those doctors who took notice. This new way of looking at what carbohydrates do to blood sugar control turned conventional medical ideas upside down. A whole range of foods that doctors thought safe, particularly for diabetics, Jenkins found to be decidedly dubious. Over the years, researchers have tested many more foods and they found that most processed foods have consistently the same index. However, fresh fruits and vegetables, which are naturally variable, can have quite a wide range of index. Even so, when all is considered, the glycemic index measure brings completely new insights into what type of foods are right for humans: we now understand that nature did not design the human body to handle foods that give a blood sugar rush.

In this book, foods that have an index in the range of 61 and above, we call “bad” carbohydrates: they consistently produce an unhealthy sugar spike. Foods with an index between 31 and 60, we call “borderline” carbohydrates: they produce sugar surges which, in a healthy person, the body controls, but only at the price of unnecessary stress to the body. Foods with an index from 0 to 30, we call “favorable” carbohydrates: they produce blood sugar levels that are within the body’s normal range for comfortable, unstressed handling.

Glycemic index scores present a few surprises. Starchy foods like bread (even whole-wheat) and breakfast cereal (corn flakes) are “bad” carbohydrates. Fruits are all over the place: pineapple is “bad,” banana is “borderline,” and raspberries are “favorable.” Unsurprisingly, non-starchy, non-sugary foods like most nuts, salads, and vegetables fit into the “favorable” category.

Another surprise is the special type of sugar called fructose—it has a favorable glycemic index and does not raise blood sugar levels unhealthily. Fructose is common in fruit, so it is not a surprise that human bodies are very well adapted to it. Fructose is not converted to glucose straight away by the digestive system; it has to pass through the liver for conversion. This slows down the rate at which it hits the bloodstream. Finally, it’s a surprise to find another sugar, maltose, that is more glycemic than glucose itself. Maltose is made of two glucose molecules joined together and, as its name suggests, is the chief sugar in malt.

There is another factor that makes a difference: the concentration of sugars and starches in the particular food. Will just one cornflake or one pineapple chunk set off a bad glycemic reaction? One supposes not, but to find out, some researchers have developed the concept of the “glycemic load.” This is an attempt to define how much of a food needs to be consumed before it triggers a glycemic reaction. They take the glycemic index (GI) of a food and combine it with the amount of carbohydrate in a standard U.S. Department of Agriculture (USDA) serving size to get the glycemic load (GL) score. A GL of 20 or more is “high,” a GL of 11 to 19 is “medium,” and a GL of 10 or less is “low.”

Of course, everything depends on the serving size that is actually consumed by a person. That is why even the concept of glycemic load has its limitations—this factor is only valid if one consumes a standard serving size. The USDA sometimes has absurdly low “normal” serving sizes. For example, a serving of spaghetti is 2 ounces (57 g) of dry weight. Most home cooks use double that quantity when serving spaghetti.

Measuring the glycemic power of foods is a useful guide and it has a direct bearing on the damage that glucose can do to our health. Nevertheless, it is one stage removed from a worse villain: abnormally high insulin levels. Because of insulin’s potential for creating havoc with our biochemistry, researchers such as human nutrition expert Susanna H. Holt have established insulin indexes for many foods.
¹¹¹
She did it in a way similar to the process for glycemic indexes: volunteers ate different foods and had their insulin levels measured over several hours.

Insulin indexes usually, but not always, rise and fall in the same rhythm with the glycemic index. Once again, there are some real surprises—some foods that might pass muster on a glycemic basis fail on an insulinemic basis. There is one further factor: proteins might not raise blood sugar levels, but they
do
raise insulin levels, some very sharply—notably, yogurt. Worse, if proteins and carbohydrates are eaten together, then the insulin raising power of the combination is much greater than of the two ingredients separately.

The table gives some typical values for an insulin index.
¹¹²
It can be seen that potato and yogurt are exceptionally “insulinemic”—that is, they have a powerful insulin-raising ability. Beef, fish, and eggs have a normal insulin-raising ability. Information like this helps build a picture of the foods that we should consider eliminating from the Savanna Model candidates.

Insulin Index
Food	Index	Category
Potatoes	124	Abnormal
Yogurt	115	Abnormal
Bread	100	Abnormal
Rice	79	Abnormal
Fish	59	Normal
Beef	51	Normal
Eggs	31	Normal

We’re not Designed to Consume Sugars

We saw in chapter 1 how the San were measured as having a low “insulin response”: this means that their fat cells do not react quickly to the instructions given by insulin. Another way of saying it is that their bodies display “insulin resistance.” Insulin resistance occurs when the body needs to produce “abnormal” levels of insulin to deal with high-glycemic foods. Australian professor Janette Brand-Miller is the icon of glycemic index research. She and Stephen Colagiuri of the University of Sydney, Australia, argue that insulin resistance is actually the naturally adapted state for human beings.
¹¹³
All peoples used to living on a primitive diet, such as the Australian Aboriginal, the Native American, and the African Pygmy, all display insulin resistance. This is normal, since the forager’s food supply does not contain glycemic foods.

In fact, this insulin resistance is helpful for reproduction. During pregnancy, glucose needs to be diverted to the fetus. Insulin-resistant females automatically maintain glucose in circulation so that the fetus can benefit from it, rather than locking it up in her own fat stores. Furthermore, during breastfeeding, the breasts develop insulin sensitivity, which encourages the uptake, by breast tissue, of glucose for conversion into the milk sugar lactose.

Most primal peoples are terribly vulnerable to the Western diet and rapidly develop diabetes, obesity, and heart disease. In a classic study, Australian researcher Kerin O’Dea returned diabetic Aboriginals to their traditional lifestyle.
¹¹⁴
Just a few weeks of living like this brought their diabetes, obesity, and poor cardiovascular vital signs back to normal.

The research on blood sugar control and insulin resistance provides powerful insights into the naturally adapted diet for humans. Clearly, nature did not design us to consume sugars and starches. This is a startling revelation for we are so used to the idea that starchy foods, such as grains and potatoes, should be part of the diet. We also see that not all fruits are entirely innocent: some of today’s fruits clearly conform to our ancestral diet and some do not. It’s clear that we have to look past the stereotypes, and at the details about what we eat, in order to understand how to navigate through our food options.

Fats and Oils

Fats and oils (“oils” are fats that are liquid at room temperature) were divided into three types: saturated, monounsaturated, and polyunsaturated. All three types are made up of fatty acids, the building blocks of all fats. Primal humans subsist on a very low-fat diet. Even so, human nutrition requires a fat intake of some kind, because the body sickens and dies if certain fatty acids are not in the diet. These are known as essential
fatty acids (EFAs), and all are polyunsaturated fats. This family can be divided into two classes called omega-3s and omega-6s.

Omega-3 EFAs are found in plants and animal matter. In plants, the most common form is alpha-linolenic acid (ALA), found particularly in walnuts, flaxseed, hempseed, and rapeseed (canola oil). In animals, omega-3 oils are particularly found in “oily” fish, such as sardines, salmon, trout, and tuna. The most common omega-3 EFAs in fish are docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Omega-6 EFAs are chiefly found in oilseed plants: for example, corn oil, sunflower oil, safflower oil, peanut oil, and soybean oil. There is only one, main omega-6 called linoleic acid (LA).

The body only needs these two classes of fat in small quantities of a gram or two (about 1/2 tsp) from all food sources combined per day. They are important because they act rather like vitamins. Indeed, at one time, we called them vitamin F
₁
and F
₂
—it is a pity that we dropped this designation, because it gives us an idea of their powerful effect on the body. The body converts these EFAs into potent types of hormones called prostaglandins. Prostaglandins are powerful agents that cause the body to do things like thicken or thin blood, increase or decrease bone building, depress or boost the immune system, and a host of other effects.

The first important feature is that what one omega type of EFA does, the other omega type does the opposite. Plus, they both use the same biochemical machinery to do their work. If one is using it, the other cannot; that is, one of them can monopolize the process to the complete exclusion of the other. This leads to a third important feature: they need to be present in the diet in a proportion of about 1 to 1—they need to be balanced. If not, one of them dominates and produces prostaglandins that, in abnormal quantities, cause sickness and disease. In the American diet, this is indeed the case. It is estimated that the ratio of omega-6s to omega-3s is about 32 to 1 instead of the ideal 1 to 1. These abnormal quantities of omega-6 fatty acids produce volumes of “bad prostaglandins” that are in part responsible for many of the diseases we see today.

Diseases Provoked by Bad Prostaglandins

Bad prostaglandins increase:

•
Blood clotting (thrombosis)

•
Bone destruction (osteoporosis)

•
Inflammation (arthritis)

•
Histamines (allergies)

•
Pain sensitivity

•
Vasoconstriction (high blood pressure)

•
Autoimmune reactions (arthritis, lupus, multiple sclerosis)

•
Hypertension (high blood pressure)

•
Bronchial restriction (asthma)