Food
The Food Pyramid
Introduction
Cut back on pasta and potatoes? Eat more olive oil? Get your calcium from a pill? We discuss the nutrition guidelines proposed by Harvard researchers.
There are often attacks on the conventional advice about what we should eat. Nothing new in that?
Well, this time the attack comes from the very heart of the establishment. It has strong scientific credentials and has been championed by one of the world's leading nutritionists. And the big casualty is that mainstay of good-eating messages, the Food Pyramid.
Overview
For over 10 years, New Zealanders have been presented with the concept of a "food pyramid", meant to represent a healthy approach to eating. The idea is simple: you're supposed to eat lots of the food at the base of the pyramid, and just a little of what's at the top.
The original Food Guide Pyramid was invented by the US Department of Agriculture in 1992, and was adapted for New Zealand by the Heart Foundation and Cancer Society.
The New Zealand version is taught in our schools as part of the health curriculum, is available on various websites, and is promoted by some health organisations. But readers may be surprised to learn that it is not part of the official guidelines for New Zealand nutrition. The reason? In some important respects, it's out of date.
The pyramid contains some key messages on which all nutrition experts agree - chief among them, that everyone should eat lots of vegetables and fruit.
But the Food Pyramid does not reflect some messages that are now known to be vital to good health. In particular, it doesn't differentiate between different types of fat, between different types of carbohydrate, and between different types of protein.
Due to its simplicity it needs to be accompanied by other messages about serving sizes and food types.
But medical researchers at the Harvard School of Public Health, led by a widely respected professor of nutrition, Dr Walter Willett, have gone a lot further than that.
Based on very large population studies and what they say happens in our chemistry when we eat (see The science of food), they have advocated that the Food Pyramid be scrapped. In its place, they have proposed a different pyramid, which they call the Healthy Eating Pyramid.
Are they right? And what do the New Zealand food health authorities have to say?
Traditional food pyramid
The Food Pyramid, as adapted for New Zealand use in the early 1990s by the Heart Foundation and Cancer Society.
Harvard's Healthy Eating Pyramid
The Healthy Eating Pyramid, as developed by Walter Willett and colleagues at the Harvard School of Public Health. 
Fats and oils
The current Food Pyramid lumps all fats and oils together at the top of the pyramid. However, there are four different sorts of fats: saturated (such as animal fat, butter, palm oil and coconut oil), trans fats (found in commercial margarines and many processed foods), monounsaturated (such as olive and canola oil) and polyunsaturated (such as sunflower oils).
In addition, canola, flaxseed, walnut and fish oils are rich in omega 3 fatty acids, and some seed and grain oils are good sources of omega 6.
Saturated and trans fats behave differently in your body from unsaturated fats. They increase the amount of "bad" cholesterol in your bloodstream, and are known as "bad fats".
Unsaturates, in contrast, actually reduce the amount of "bad" cholesterol. Along with omega 3 and 6 fats, they are called "good fats" (see The science of food).
What's at issue is whether you can have too much of a good thing. Most nutritionists say it's important to cut back on saturated and trans fats and on your overall level of fat consumption.
But the Harvard team has proposed that good fats belong at the bottom of the pyramid. They say liquid oils like olive, canola, soy, corn, sunflower and peanut should be eaten daily. This is a radical departure from the established view, because it doesn't say we should eat less fat overall - in fact, it puts greater emphasis on oils than vegetables.
To support their argument, they point to the diets of people in Japan, Finland and Crete. The traditional Japanese diet contains only 10 percent fat, and the rate of heart disease among men is around five percent.
In Eastern Finland there is about 38 percent fat in the traditional diet. It's mainly saturated (from dairy products) and it leads to a whopping 30 percent rate of heart disease among men. But in Crete, where they eat around 40 percent fat, mainly from olive oil, the heart disease rate among men is an astonishingly low two percent.
However, it's important to remember that the traditional Mediterranean diet includes a lot of fruit, vegetables and fish, and that diet isn't the only issue. Other lifestyle factors, like smoking and exercise, also play important roles.
All the New Zealand nutritionists we spoke to disputed the Harvard view that people should eat large amounts of unsaturated fats.
Suzi Penny, of the Institute of Food Nutrition and Human Health at Massey University, says putting "good fats" on the bottom layer of the pyramid is likely to significantly increase the problems of obesity. These include a greater risk of type 2 diabetes, strokes and other illnesses, as well as heart disease.
"All fats, whether they are monos, polys or omegas, provide the same amount of energy, which is double that of carbohydrates. Dipping bread in olive oil instead of butter is great, but in large amounts and often, it means weight gain for those who may not need the extra kilojoules."
Willett says the correlation of high intakes of fat and high rates of heart disease is limited to saturated fat. He adds: "No study has demonstrated long-term health benefits that can be directly attributed to a low-fat diet."
Who is right? In our view, the evidence for eating lots more unsaturated fats is inconclusive. But the critical message is that saturated fats and trans fats are bad. Cut these back in your diet, and you'll be taking an important step towards healthy eating.
Carbohydrates
The Food Pyramid and most nutritionists say we should eat plenty of carbohydrates like potatoes and the cereals food group, which includes rice, pasta and bread. But some cereals are much more refined than others. When they are refined they can lose some of their food value, and can also be combined with trans fats (as in commercial baking).
There's not much debate about this in itself, but there is a big disagreement about its significance.
The prevailing view is that it doesn't matter too much. Wholegrain cereals are best, but if your diet (or your kids' diet) gets its bulk from breakfast cereal or toast, sandwiches, and pasta/rice/spuds for dinner, you'll probably have a good basis on which to work. Of course, that's provided you don't use cereal just as an opportunity to eat sugar, and sandwiches just as an opportunity to eat butter!
Willett says this is wrong. The Harvard view is that wholegrain foods should be eaten "at most meals", but that refined carbos, in which they include white rice, white bread, pasta and potatoes, should be eaten "sparingly".
Willett says a diet high in refined carbohydrates is fuelling the rapid increase in diabetes, heart disease and obesity now taking place throughout the Western world.
Most nutritionists agree that it's wrong to eat lots of simple and refined carbohydrates. Instant noodles, most biscuits, cakes and muffins, some sugar-coated breakfast cereals and the like may be carbo-based, but they're not healthy choices.
But white bread is not high in sugar and fat (although many toppings are), and nor is white rice or pasta.
Nutritionists criticise the Harvard researchers for praising the traditional Asian diet, while seemingly ignoring the fact that it is based on white rice. Similarly, they note that many - but not all - Mediterranean diets are based on pasta and white bread.
In our view, it makes sense to switch to wholegrain carbos if you can. One of its key values is that it's very filling, so you eat less overall.
But if you don't like wholegrain foods (or your kids won't even eat them), you probably shouldn't fret. For one thing, there's no point in trying to eat a diet of food you don't like. You'll just give up.
For another, it's obvious there is a difference between refined carbos that are low in sugar and fat, and those that are not. Don't give up on bread, rice and pasta.
The humble spud
What about potatoes? They're a good source of vitamins, minerals and fibre - but, as the Harvard team says, a boiled potato will raise your blood sugar levels more than the same amount of energy in table sugar.
This is because potatoes are mostly starch, which is quickly broken down to glucose. Table sugar is made up of glucose and fructose, and the fructose takes longer to convert to glucose. This leads to a slower rise in blood glucose levels.
But does it follow that potatoes should be eaten "sparingly", as Willett suggests? We doubt it. Potatoes are normally eaten as part of a meal, together with protein, fat and fibre. These all slow the rise in blood glucose - plus you get the value of the potato's other nutrients.
Sugar, however, often comes by itself in sweets and chocolate, so the rise in blood glucose will be quicker.
Potatoes have a useful role in a healthy diet. But go easy on the butter, and avoid chips fried in animal fats or palm oil!
Protein, fruit and vegetables
Protein
The current Food Pyramid puts all proteins in the middle. The Harvard version separates them into red meat at the top, and other protein sources which it places further down.
Red meat can be high in saturated fat, which is why Willett puts it at the top. But some cuts of meat are far fattier than others, and these are the ones to avoid. Neither pyramid reflects this.
Processed meats, like salami, sausages and bacon, are also high in saturated fats, while lean red meat is an important source of iron.
Fish and shellfish are healthy protein sources. They have little saturated fat, and if the fish is oily, like salmon or sardines, it will be rich in omega 3. Everyone agrees this increases the heart-healthy benefits.
Chicken has a thick layer of fat in and just under the skin, and you'll also find lumps of fat clinging to various parts of the body. Get rid of these, and it's generally agreed chicken is a healthy source of protein.
Nut oils are unsaturated, and therefore in the "good fat" category. But since they are high in fat, the prevailing view is to eat them sparingly. Willett says nuts, along with other plant proteins like soy and beans, should be eaten in up to three servings a day. (Note that he is not talking about salted nuts or nuts cooked in animal fats!)
Nuts, like most other protein sources, are more filling than other foods, which is probably why high-protein diets are known to lead to short-term weight loss (see What about Atkins and the Zone?).
There are several useful messages to draw from all this. First, choose a variety of lean meat and poultry. Second, substitute fish, nuts and other plant proteins as often as you can.
Third, limit the size of your portions. Nutritionists agree that protein, whatever its source, should not form the bulk of your meals.
Fruit and vegetables
Eating lots of fruit and vegetables is not controversial. Fruit and veges are the main source of many of the vitamins, minerals and fibre needed for good health. They are also a significant source of antioxidants.
And because they are low in kilojoules they're good to fill up on.
Dairy products
The Food Pyramid says we should eat moderate amounts of dairy products like milk, cheese and yoghurt. On the one hand, dairy products contain saturated "bad fat". Some, like soft cheeses, have it in large amounts.
But on the other hand, dairy is rich in calcium, a mineral essential for strong teeth and bones. And milk is low in fat - in fact, many milks and yoghurts are extremely low.
At Harvard, they've cut the recommended amount back. They claim there is no evidence calcium from dairy foods keeps bones strong. In fact, they say the highest rates of bone fractures are seen in countries with high dairy consumption. They also point to studies suggesting a link between some cancers and high dairy intake.
In the Harvard pyramid, just one or two servings a day are suggested. They say we can get the calcium we need from wholegrains and legumes (soy, beans and the like), and/or from a calcium supplement.
These are startling claims. Most people don't eat enough wholegrains and legumes to satisfy their calcium needs. And it's generally thought that food nutrients should be taken in food, rather than pills, because this gives them a better chance of working properly.
Osteoporosis New Zealand says there are many studies showing dairy products are beneficial for bones and teeth. In a study published this year women with a low milk intake during childhood had double the risk of getting fractures. A Massey University study says milk replenishes the calcium and phosphate lost after consuming sugary drinks.
Several foods (including some biscuits, drinks and cereals) are now fortified with calcium. But often they also contain a lot of sugar. And dairy foods contain other nutrients, including phosphorus, vitamin A and zinc.
In our view, although more research is required, there is a lot of evidence for the value of low-fat (and calcium-enriched) dairy products.
Supplements
Vitamin supplements don't appear in the Food Pyramid and the orthodox view is that unless you have a nutrient deficiency that cannot be addressed by diet, there's little to gain by taking pills.
Willett, however, advises a regular dose of multivitamins for most people.
The relevance for New Zealanders is hard to see. The National Nutrition Survey 1997 concluded that, in the general population, vitamin intakes from food were satisfactory. It's also known that once you reach optimal levels, especially for the B vitamins and vitamin C, you will simply get rid of any excess in your urine.
There is also evidence that antioxidants in food are more effective than in supplements.
Some people do need specific dietary supplements. Vegans need extra vitamin B12; people who get very little exposure to sunlight need extra vitamin D. Women planning a pregnancy, and those who are newly pregnant, should take folate (folic acid) pills.
Alcohol and exercise
Alcohol
Alcohol fits in the top of the current pyramid. But many studies have shown moderate drinkers (one to two drinks per day) have healthier hearts and live longer than heavy drinkers or teetotallers. These findings were initially linked to red wine, but the effect seems to hold for all alcoholic drinks.
The Harvard researchers have reflected this by including alcohol "in moderation" further down their pyramid. They note the exceptions - children should not be drinking, of course, and many other people simply don't want to, and should not be expected to. They also make it clear that while moderate amounts are good, too much is not.
These recommendations are controversial, especially as many health experts argue it's wrong to give any pro-alcohol message.
Alcohol contributes to death and injury on the roads and other accidents. The Cancer Society says it may contribute to cancers of the mouth, upper digestive tract, liver and breast.
And the benefits of alcohol are not known to be universal. The lower risk of heart disease has been specifically linked only to certain groups, including postmenopausal women and men older than 45 years of age.
Exercise and weight control
The messages of the Food Pyramid are limited to food. But the Harvard pyramid recognises two other critical issues: that good health also involves regular exercise, and that the overall message should be to limit your food intake.
Again, these messages are not controversial, and it's agreed the current pyramid is inadequate for not including them.
What sort of exercise? It probably doesn't matter, as long you do it regularly.
And what sort of limits should there be on food intake? Put it this way: one reason people in the West are fatter is that we just eat too much. For many people, cutting back on the kilojoules, from whatever source, is the key.
The science of food
We eat for energy and for nutrients to keep various parts of our bodies functioning. Different foods meet these needs in different ways.
Excess energy from all foods is stored in the body as fat. All carbohydrates are converted to glucose and when glucose is carried in the bloodstream, after eating, it stimulates the pancreas to produce insulin. It's insulin's job to transport the glucose into cells where it's used for energy or stored, if it's not needed straight away.
When you eat a simple carbohydrate (as in the sugars in fruit and other sugary foods and drinks), the metabolism into glucose happens very quickly. Complex carbohydrates, such as those found in wholegrain cereals, take longer to convert to glucose. That's why a big bowl of porridge will keep you going all morning.
How fat works
Because the body stores energy as fat, when you eat fat, it's already in a form that makes it easy to store. This means energy from fat is the first to be stored and the last to be used. It worked well for our cold and hungry ancestors who had to hunt to stay alive, but it's really not useful if you work at a desk all day.
However, the type of fat you eat is important because it affects the amount and type of cholesterol in your blood.
Cholesterol is found in the blood in two types of packages - low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs).
LDLs are liable to deposit cholesterol as fatty streaks on your artery walls. Those streaks can build up and narrow the arteries. Also, saturated fat can make the blood cells stickier, so they form a clot. A blood clot in the heart will cause a heart attack; in the brain it will cause a stroke. Saturated and trans fats increase the LDLs in your blood (and trans fats also lower the HDLs). They're the "bad fats".
HDLs do just the opposite - they carry cholesterol out of the tissues and back to the liver for processing. Monounsaturated and polyunsaturated fats decrease the LDLs, so are heart-healthy fats.
The orthodox view is that we should replace saturated fat in our diet with carbohydrates. But the Harvard researchers disagree. They argue that the key to reducing heart disease and the risk of other illnesses is the ratio of LDLs to HDLs. They say that when saturated fat is replaced by carbohydrates, the LDLs fall but so do the HDLs, so the ratio doesn't change much. It's only when you replace saturated fat with unsaturated fat, that you get a significant change in the ratio.
According to Willett, it's not a low-fat diet you need, but a low saturated/trans fat diet.
However, there's an even more important message to take from this. The body is not going to store unwanted energy as fat unless you eat more food than you need. As Willett says, "the best way to avoid obesity is to limit your total calories [kilojoules]".
It's a message that has wide support, and it's a hard thing to achieve if you're eating lots of fat - of any kind.
How do they know?
It's not easy to find out how food works in the body. Several types of trials and studies are used.
Randomised controlled trials
are the best method for assessing the effects of diet on health. In a large trial, individuals are randomly given one diet or another and followed for many years. The results can be persuasive, but running such trials is expensive and sometimes impractical.
Case control studies
involve patients with a certain disease, like cancer, being asked about their earlier diets. They are compared to a population group without the disease. This can provide in-depth information, but is subject to biases.
Epidemiological research
involves the study of large populations. This is the reverse of a controlled trial, in that you start with outcomes and look for causes.
Biochemical research
involves laboratory study to determine what happens in the body.
The Harvard research leans heavily on two epidemiological studies: the Nurses Health Study, begun in 1976 and involving 90,000 women, and the Health Professionals Follow-Up Study in 1986, involving 50,000 men. These studies found the risk of heart disease was strongly influenced by the type of dietary fat consumed, but not the overall amount.
These are very large studies and can be expected to produce robust results. But they still need to be approached with caution. Nurses and doctors are not necessarily representative of the whole population. And from a New Zealand point of view, the fact they are American studies may make them less relevant here.
The official view
The Ministry of Health's guide Healthy Eating for Adult New Zealanders reflects some of the thinking behind the Food Pyramid, but does not actually include the pyramid. It says:
- Eat a variety of foods from each of the four major food groups each day. This includes vegetables (at least 3 servings), fruit (at least 2), breads and other cereals (at least 6), dairy products (at least 3), protein such as lean meat, chicken, seafood, eggs, beans and lentils (at least 1 serving).
- Eat foods low in fat (especially saturated fat), salt and sugar.
- Maintain a healthy body weight by regular exercise and healthy eating.
- Drink plenty of liquids each day, especially water.
- If drinking alcohol, do so in moderation.
The key differences between this list and the Harvard approach are:
- The MoH does not advocate that large amounts of unsaturated fats should be eaten daily.
- It says nothing about the different sorts of carbohydrates and proteins.
- It does not address the issues surrounding dairy foods or supplements.
What about Atkins and the Zone?
If you're an advocate of a low-carbo diet like the Zone, or the high-fat, high-protein Atkins diet, you're probably already shouting, "I told you so!"
Indeed, the Harvard research seems to validate some of what these diets propose. "In randomised trials, individuals assigned to low-fat diets tend to lose a few pounds during the first months but then regain the weight," says Willett. "In studies lasting a year or longer, low-fat diets have consistently not led to greater weight loss."
The Zone and Atkins both say that cutting out fat is not the key to weight loss. But the Harvard researchers do not advocate their low-carbo approach. Willett says wholegrain carbohydrates are extremely important. And he does not accept the Atkins view that you can eat large amounts of protein.
There are other problems with both the Zone and Atkins. The Zone is meticulous about quantities, which makes it very difficult to follow. Atkins is worse, because it encourages the consumption of both saturated and trans fats.
You might lose weight on either diet - but it could be in large part because you are eating less overall. But Atkins in particular may also increase your risk of other health problems, especially if you have kidney problems or are already at risk of heart disease.
Where does this leave us?
The debate about food and health is not going to go away. Nutrition is a changing science and we are continuing to learn how food works in the body.
Our advice
- If you're overweight, try to cut back the total quantity of food you eat. This is probably the single most important piece of dietary advice to consider.
- The Harvard pyramid has some valuable messages, including: that there is an important difference between "good" and "bad" fats; and that highly refined, sugar-laden foods should be eaten sparingly.
More help
The National Heart Foundation; 09 571 9191.
Diabetes New Zealand; 0800 342 238.
Cancer Society of New Zealand; 04 494 7270.
Osteoporosis New Zealand; 04 499 4862.