Nutrition 331: Nutrition for Health

Study Guide: Unit 15

What Is the Healthiest Diet?


The great 17th‑century physician, Boerhaave, kept an elaborately bound volume that was said to contain all the secrets of medicine. When it was opened after his death, all the pages were found to be blank, except one. Inscribed on this page was but one sentence:

“Keep the head cool, the feet warm and the bowels open.”

Here we review what we have learned in the course and summarize the quantities of the “healthiest” diet. It should be clear from the preceding units that chronic diseases are associated with a diet high in sugar and sodium and low in dietary fibre.

The rational approach to the question of chronic diseases is primary prevention based on a healthy lifestyle, particularly good nutrition. The evidence we have presented reveals that essentially the same diet prevents virtually all of the major chronic diseases. Furthermore, the evidence leads us to conclude that some of the chronic diseases are potentially reversible, and that diet can make a major contribution towards this reversal. However, the appropriate diet for disease reversal is stricter than that for primary prevention.


After completing this unit, you should be able to

  1. describe the key features of a diet that offers maximal protection against chronic diseases of lifestyle.
  2. Identify the major problem areas commonly observed in the diets of Canadians.
  3. discuss the role of non-dietary lifestyle choices in causing or reducing risk of chronic diseases.
  4. identify the benefits of a population approach to healthy eating vs. a high-risk approach.
  5. discuss how diets can be adapted to reduce harmful effects on the environment.

Section 1 The Canadian Diet Today

Various surveys have painted a picture of the typical Canadian diet. A large survey suggested that the following aspects of the diet are important problem areas (Kirkpatrick & Tarasuk, 2008):

  • Intake of dietary fibre is about 15 grams/day for women and 19 grams per day for men. This is considerably below the adequate intake of 25 and 38 grams per day, respectively.
  • It is very common for the intake of vitamin A to be well below recommended levels.
  • A low intake of iron is common among women.
  • Older adults, especially women, commonly have a low calcium intake.
  • A low intake of potassium, folate, and vitamin B6 are common, especially among women.

The survey also showed that the nutritional quality of the diet is considerably worse among people living in poverty than among more affluent people. Numerous other studies reveal that dietary problems may be very common for several other areas of the Canadian diet, including intake of fruit and vegetables (see Section 2), omega‑3 fat (see Section 3), and vitamin D (see Section 5). In each of these cases, there is a dietary inadequacy. Sodium poses the opposite problem—one of dietary excess (see Section 5).

Section 2 Whole Grains, Fruits, and Vegetables

The majority of the diet should consist of whole grains, fruit, and vegetables. A major advantage of such a diet is that it is typically high in fibre plus the many micronutrients and phytochemicals that come with these foods. Recall from Unit 5 that Canadians typically consume about half of the recommended fibre intake.

Potential problems with a high fibre diet include the acceptability and palatability of the diet, especially if it creates abdominal discomfort. This often occurs when people suddenly change from a low fibre to a high fibre diet. Fibre should be increased gradually and more fluids drunk to minimize abdominal discomfort. As an adequate intake of fibre can be easily consumed through a healthy diet, healthy people seldom need fibre supplements.

Previous units have repeatedly emphasized the major health advantages of a generous intake of fruit and vegetables. These foods are rich in antioxidants and phytochemicals. Studies indicate that people with a generous intake of foods rich in these substances have a reduced incidence of conditions including age-related blindness (macular degeneration and cataracts, textbook, pp. 256 & 637), pulmonary disease, and loss of cognitive ability in the elderly (Temple, 2000).

Taken as a whole the findings from cohort studies indicate that each extra daily serving of fruit and vegetables lowers risk of death by 5% (Wang et al., 2014). This implies that if people who have a relatively low amount of fruits and vegetables, say 2 servings a day, could be persuaded to increase this to 5 servings a day, their risk of death would drop by a remarkable 15% over the next 10 or 20 years.

Researchers and scientists continue to study the question, “How much fruit and vegetables are needed for these health benefits?” The exact answer is not clear. For cancer prevention, the guideline is 400–800 grams per day. This translates into a minimum of five servings daily. Nutrition surveys of Canadians consistently show that about half the population does not consume this amount (Steele, 2005).

How do juices fit into this? Orange and apples juices contain a similar amount of sugar as do cola drinks. For that reason these foods can also induce overconsumption of energy. However, as they also supply all the other nutrients present in fruit, they are obviously preferable to cola drinks. In other words, while whole fruit is preferable because of its fibre, fruit drinks are an acceptable part of a healthy diet.  Tomato and other vegetable juices typically contain about half as much sugar as that present in fruit juices.

Reading Assignment

Optional reading: Read pages 64–72, Controversy 2: “Phytochemicals and Functional Foods: What Do They Promise? What Do They Deliver?” of Chapter 2: “Nutrition Tools—Standards and Guidelines.”

Note: You will not be tested on this material.

Our understanding of food and of the health effects of the many substances supplied by food is in transition. This reading discusses many of the controversial concepts.

Section 3 Dietary Fat

The recommendation to consume 20–35% of calories from fat serves a range of people well, from the underweight to obese. The minimum level provides enough fat to meet the needs for essential fatty acids and some vitamins, such as vitamin E.

Infants and young children have different needs for fat than do adults. An infant should receive about 40% of energy from fat. Nutritionists recommend that children under the age of two years should drink homogenized (full fat) milk to help satisfy their energy needs. Dietary fat should gradually decrease from one year of age through the teen years to the recommended ranges for adults.

For many years, nutritionists and people who write about health issues have been advocating the benefits of low-fat diets. However, low fat is not always a healthier choice. Many fat-reduced foods, such as some brands of low fat yogourt, have the fat replaced with sugar or purified starch. As a result, these products may be no healthier than the regular varieties. A low-fat diet, if taken to an extreme (e.g., 15% or less energy from fat), can be too low in essential fats.

Unsaturated fats contribute to the prevention of heart disease (Unit 12). While the link between saturated fat and risk of CHD is now considered to be weak, the prevention of CHD is best accomplished by replacing saturated fat with unsaturated fats. Trans fat is the worst of the different types of fat as it is clearly a risk factor for CHD. It is mostly found in processed foods such as fried foods, cookies, cakes, doughnuts, chips, and hard margarine. Fortunately, many foods have now been reformulated with a reduced content of these fats.

A body of convincing evidence has steadily accumulated in recent years showing that omega‑3 fat is of major importance. Lack of this nutrient may be one of the most common nutritional problems in today’s Canadian diet. This illustrates the potential harm of being over-zealous with a low-fat diet: it can cause the diet to be even more inadequate in omega‑3 fats. The best source of omega‑3 fat is fatty fish, which manifests a clear and consistent protective relationship with risk of heart disease.

Section 4 Meat, Fish, and Alternatives

As was discussed in the previous unit, strong evidence indicates that the diets of many people would be healthier if they consumed less red meat, especially processed meat. Fish is preferable while poultry lies in-between. Alternatives, most notably legumes and nuts, are excellent substitutes for meat.

Section 5 Sugar

It has been well-known for decades that sugar plays an important role in tooth decay, particularly when the sugar is eaten in a sticky form, as in candy. A great many studies have been conducted in recent years that shed light on the relationship between sugar intake and other aspects of health. As we discussed in Unit 5, sugar has a poor ability to satisfy the appetite. Consequently, it encourages overeating and excess weight gain. In the last few years, findings from cohort studies have been published that indicate that sugar significantly increases the risk of both diabetes (Malik et al., 2010) and CHD (Fung et al., 2009). The strongest evidence pointing to sugar as a causative factor in obesity, diabetes, and CHD is seen for sugar-sweetened beverages, such as cola drinks.

Another concern with sugar that it supplies “empty calories” (i.e., it offers no nutrients except energy). As such, it displaces vitamins, minerals, and dietary fibre from the diet.

There is no clear recommendation for limiting sugar. One recommendation proposed by the DRI committee suggests that sugar could provide up to 25% of energy intake as long as the person is meeting their nutritional needs and not exceeding energy needs. This recommendation has been much criticized by nutrition professionals as high sugar foods often replace nutritious foods, and few Canadians need extra calories. A World Health Organization guideline recommends less than 10% of calories from simple sugars. The American Heart Association is more restrictive, recommending an amount equivalent to about 5–6% of dietary energy. A reasonable target is that sugar intake should not exceed 10% of energy with 5–6% being preferable, especially for persons where controlling sugar is important such as those who are overweight or at risk of diabetes or CHD. Note: This figure refers to added sugar, not to sugar naturally present in foods such as fruit.

It is important to recognize the major sources of sugar in the diet. The dominant source of sugar comes from sugar-sweetened beverages, such as cola drinks. This includes all beverages bearing labels such as punch, beverage, or cocktail.

Therefore, sugar consumption should ideally be reduced from present levels. A cola drink contains about 11 or 12 grams of sugar per 100mL which means that a can (33mL) delivers about 36 grams or 145kcal of sugar. Thus, an adult with a typical energy intake (2000–2500kcal per day) who drinks a can of cola every day will obtain about 6–7% of his or her energy from this one source. Based on the recommendation that intake of sugar should be limited to 5–10% of energy intake, that means that one can of cola (or the equivalent amount of sugar from other sources) should be the upper limit of daily intake for most people. As discussed earlier, fruit juices resemble cola drinks in terms of their sugar content but are far preferable.

An interesting development in recent years is Vitamin Water. This product, produced by the Coca‑Cola Corporation, is displayed prominently in supermarkets and corner stores across Canada. The beverage, which comes in several varieties, contains vitamins plus herbs. While the sugar content is only about half of regular cola drinks, it is still basically sugar water. It is perhaps one of the most brilliant examples of rebranding in corporate history. At a stroke, Coca‑Cola has been transformed from a beverage widely seen as synonymous with junk food into a beverage that gives an impression of being healthy (as long as one doesn’t scrutinize the label).

Section 6 Sodium and Salt

Sodium in the diet should be limited to the Upper Limit of 2300mg per day. This is about 25–50% less sodium than that consumed by the average Canadian daily. There is strong evidence demonstrating a major role for sodium in hypertension. Excess dietary sodium is also linked to stomach cancer, as indicated in the Unit 13. Because of these dangers, an intake of 1500 mg per day is a sensible target.

The role of food manufacturers is especially important in reducing sodium intakes, as around 75–80% of dietary sodium comes from salt added during food processing.

Section 7 What is the Healthiest Diet?

Reading Assignment

Read pages 498–500 “Food Feature: Diet as Preventive Medicine” of Chapter 11: “Diet and Health.”

Review Eating Well with Canada’s Food Guide.

“Food Feature: Diet as Preventive Medicine” provides an excellent summary of the key recommendations for healthy eating. But as with other sections of the textbook this reading exaggerates the importance of saturated fat.

What is the healthiest diet? To answer this question, we are reviewing some meal plans that provide recommendations for amounts and types of foods, not nutrients.

Review Section 1 of Unit 9. That unit explained the concept of dietary patterns. Unit 9 clarifies the strong reasons for focusing on dietary patterns, rather than individual nutrients.

We encourage students to use Canada’s Food Guide as a dietary guideline. It helps people choose appropriate amounts and types of food. While the Food Guide may have some weaknesses, following its guidelines should meet most protein, vitamin, and mineral needs, and encourage an adequate fibre intake.

Vegetarian diet plans are also available to recommend guidelines for appropriate nutrient intakes as well as fibre (see textbook, pp. 242–243).

The Mediterranean diet is often used as an example of what people should aspire to eat. Cohort studies have revealed a consistent pattern that persons adhering to the Mediterranean diet have a lower overall mortality as well as lower rates of both cardiovascular disease and cancer (Sofi et al., 2010). There are many attributes of a Mediterranean diet that provide health benefits. The key ones are believed to be: the use of olive oil as the main fat in food preparation; a high consumption of legumes, fruits, nuts, and vegetables; and a low consumption of meat and increased consumption of fish.

In Canada, agencies advocating for Canadians to lower their risks for heart disease, cancer, osteoporosis, and type 2 diabetes support Canada’s Food Guide. Consequently, Canadian health professionals can speak with confidence when educating clients and professionals on using it. The challenge in a world with instant information is that the Food Guide seems conservative, not cutting edge. Tried and true does not always have mass appeal. This is unfortunate, because the “tried and true” Canada’s Food Guide is helpful for almost all Canadians over two years of age.

A solid body of evidence has emerged showing that a large section of the Canadian population would benefit from supplemental intake of vitamin D. In Units 9 and 10, we looked at the importance of vitamin D in protecting against osteoporosis (most common in older women) and the associated risk of fractures. In Unit 13, we discussed the exciting evidence that strongly suggests that vitamin D has the potential to prevent a significant fraction of cases of cancer, especially colon cancer. Evidence has also appeared indicating that vitamin D may be valuable in protecting against several other conditions, including heart disease and type 2 diabetes. It must be stressed that many of these potential benefits of ensuring an adequate intake of vitamin D are yet to be confirmed.

As we saw in Unit 13, with respect to cancer, the ideal dose of vitamin D for preventive purposes is well above the RDA (currently 15 micrograms [•g] or 600IU per day at ages up to 70). A supplemental dose of 25 micrograms (or 1000IU) per day is indicated for the prevention of the diseases mentioned above. This supplementation is primarily for people who have inadequate exposure to the sun, including the great majority of Canadians. In 2007, the Canadian Cancer Society endorsed this viewpoint. The Canada Food Guide (2007) recommends that all adults over age 50 should take a supplement supplying 10 micrograms (or 400IU) of vitamin D per day.

It is important to note that the potent form of vitamin D is D3. Many supplements have D2, which is only one quarter as potent as D3.

Section 8 The Role of Nondietary Factors

Apart from diet, other factors play a major role in the causation and risk reduction of chronic disease. Smoking is, of course, of massive importance. It plays a major role in several cancers (particularly lung) and in CHD. If one is advocating a healthy lifestyle, whether for prevention or treatment, discussing the importance of diet while ignoring smoking is fighting with one hand tied behind one’s back.

Passive smoking—breathing other people’s cigarette smoke—also affects one’s health. Passive smoking causes a significant number of cases of CHD, lung cancer, respiratory disorders, and other health problems.

Aerobic exercise can slow down the development of various chronic diseases. It burns up energy, which plays an obvious role in the prevention and treatment of obesity. Exercise is also particularly important in preventing diabetes and CHD. Exercise also helps to prevent and treat hypertension. There is strong evidence that exercise reduces the risk of cancer of the colon and breast (post-menopausal) by at least one-third (WCRF/AICR, 2007). Weight-bearing exercise is protective against osteoporosis.

What is an appropriate recommendation for the amount of exercise?  The Canada Food Guide (Figure 2‑4 on p. 44 of the textbook) suggests that adults accumulate at least 2 hours and 30 minutes of moderate to vigorous physical activity each week.  The weight of evidence suggests that an hour per day, on average, is closer to optimal.

Section 9 Diet and the Prevention of Disease

The major health problems faced by people in affluent countries are chronic diseases of lifestyle (CDL). Over the last few decades, medicine’s efforts to combat these diseases have largely taken the form of looking for new and more effective therapies, particularly drugs. However, there have been relatively few successes. For instance, the five-year survival rates for some common cancers (lung and pancreas) have improved little over the past 40 years (Welch et al., 2000). Only in limited areas has real progress been made. For example, therapies for some of the less common cancers, particularly those of children and young adults, have seen dramatic progress. New and more effective drugs are now available for peptic ulcers and hypertension. However, these advances have made very little impact on the overall health statistics. In the same period, there has been an increasing realization that CDL are intimately related to lifestyle and are preventable. Taking these facts together compels the conclusion that the most appropriate strategy to counter the majority of CDL is risk reduction based on a healthy lifestyle.

The importance of risk reduction is underlined when we recall that health costs have been steadily escalating. Federal and provincial governments can no longer afford to provide unlimited medical services. It is, therefore, of paramount importance that determined efforts are made to prevent disease. However, even if the budget for medical services were unlimited and effective treatments were available for all chronic diseases, it would still be far preferable to prevent disease. Even when a victim of a disease such as cancer or stroke is successfully treated, there is still much suffering. In reality, cures will never be available for all CDL: a common first symptom of diseases such as stroke and CHD is sudden death.

The potential impact of an effective risk reduction strategy on the health of Canadians is difficult to exaggerate. With cancer, the leading cause of death, diet is estimated to cause about one-third of cases. CHD is the second leading cause of death in Canada. Diet is a major factor responsible for CHD as well. The third leading cause of death is stroke, and here again, diet is a major factor. With nonfatal disease, too, diet is of great importance. In such conditions as obesity, diabetes, colon disorders, and tooth decay, diet has a central role. Clearly, therefore, a healthy diet has the potential to prevent a vast amount of disease.

Two strategies have been proposed for implementing dietary guidelines. The first is the high-risk approach, which targets persons at high risk of particular diseases. The second is the population strategy, which focuses on the entire population.

The first step in the high-risk approach is the identification of those at high risk, usually by screening large sections of the population. In the case of heart disease, such screening leads to the identification and treatment of persons with a high blood LDL cholesterol level, especially if they also smoke and suffer hypertension. This approach is relatively cost effective as efforts are concentrated where they can do most good. Also, high-risk people have a greater incentive to adhere to advice than do those at average risk, and this fact also helps to make the high-risk approach cost effective.

The major problem with this approach is that it misses most future cases of disease (Rose, 1992). For example, the 15% of men with elevated risk factors for heart disease account for only 32% of cases. In other words, two cases out of three occur in those who would not be eligible for preventive treatment by the high-risk approach. It follows that the only real way to make a major impact on such diseases as CHD is the population strategy.

The high-risk approach is attractive to physicians as it categorizes people into “healthy” and “unhealthy” groups, and then applies treatment only to the unhealthy. After all, physicians spend their working days treating sick people so why not apply the same principle to prevention? A major flaw in this attitude is that such a division of people is artificial. For example, the classification of people into those with hypertension and those with normal blood pressure is based on arbitrary cut-off points. In reality, there is a progression from normal blood pressure to high blood pressure; hypertension is really a matter of degree. The same goes for weight, blood LDL cholesterol, and alcohol intake. The population approach recognizes that it is the population as a whole that is unhealthy and needs treatment. Simply described, our way of life, on average, does not support healthy choices.

An example of the importance of the population approach was given in Unit 12, when we pointed out that reducing the salt intake of the whole population—thereby lowering the average person’s blood pressure—would do more to prevent stroke and CHD than treating all people with hypertension.

In summary, therefore, the most sensible strategy in combating disease, especially CDL, is risk reduction. In this battle, nutrition will play a major role. Recommendations for healthy eating are likely to be the trend of future health care.

Section 10 Nutrition and the Environment

No account of a healthy diet is complete without considering an environmentally friendly design. Here are some guidelines to follow. The single biggest dietary change that we should aim for is reducing our consumption of meat. This is because meat production requires huge amounts of land, energy, and water resources. In this regard, meat from four-legged animals is worse than chicken. In contrast to meat, beans and lentils are much more environmentally friendly, not to mention their nutritional advantages. To reduce transportation costs, people should, where feasible, buy food grown close to home. Another important environmental consideration is packaging. Attempt to buy food with minimal packaging that can be recycled. If food is packaged, then larger volume packages are preferable to smaller ones. Bottled water is an especially environmentally unfriendly product, particularly brands transported from distant locations. The textbook gives some further helpful advice on protecting the environment through our food choices (p. 677).

Another environmental issue involves organic foods: foods grown without synthetic pesticides. While reducing one’s intake of pesticides is certainly positive, the quantities consumed from conventionally grown food are extremely small. Also, organic foods are usually much more expensive than regular supermarket food, typically by 50% or more. This extra cost is probably an unjustified expense for most of the population.

A Final Word

We hope this course has helped you improve your dietary habits. While knowledge is very important for making healthy choices, attitudes and behaviours also drive our daily choices. Encouraging healthy attitudes and behaviours involves both psychology and influence in a wide variety of circumstances. Early in the 21st century, health and education professionals are working to improve the availability of healthy food choices in schools. This is just one influential setting. What about the healthy food choices in convenience stores, cafeterias, and restaurants? We have many challenges to help Canadians choose a diet higher in fibre, vegetables, and fruits and lower in calories, sodium, and trans fats.

Assignment 2: Nutrition Issue Evaluation

If you have not already done so, please complete and submit Assignment 2: Nutrition Issue Evaluation via the  assignment drop box for Assignment 2. This assignment is worth 15% of your final course grade.

Final Exam

If you have not already done so, you should arrange to write the final exam. Instructions for applying to write exams can be found in your Student Manual.