Maintaining a healthy, balanced diet is essential for overall well-being and disease prevention. In the United States and other developed countries, where the average woman can expect to live 80 years or more, consuming enough calories to sustain, build, and repair the body is not sufficient. A healthy dietary pattern emphasizes whole-grain foods, legumes, vegetables, and fruits, while limiting refined starches, red meat, full-fat dairy products, and foods and beverages high in added sugars. Diet is just one piece of the puzzle; limiting caloric intake to maintain a healthy weight, exercising regularly, and not smoking are other essential strategies.
Understanding the Key Nutrient Groups
A balanced diet comprises six key nutrient groups, each playing a vital role in maintaining health. These groups must be consumed in appropriate amounts.
- Proteins: Essential for growth, repair, and general maintenance of the body.
- Carbohydrates: The primary energy source for the body. Opt for slowly digested carbohydrates rich in fiber, vitamins, minerals, and phytonutrients found in whole grains, fruits, vegetables, and beans.
- Lipids (Fats): A rich source of energy, crucial components of cell membranes and signaling molecules, and act as insulators for neurons (nerve cells) as myelin. Focus on healthful unsaturated fats from vegetable oils, seeds, nuts, whole grains, and fish, especially omega-3 fatty acids, which are essential for cardiac health. Limit trans and saturated fats, which can negatively impact cardiovascular health.
- Vitamins: Vital for a range of biochemical reactions. An optimal diet generally provides all the necessary vitamins.
- Minerals: Important for maintaining ionic balances and many biochemical reactions. Calcium is crucial for maintaining bone strength, along with physical activity and vitamin D.
- Water: Crucial for life. Metabolic reactions occur in an aqueous environment, and water acts as a solvent for other molecules to dissolve in. The ideal beverage provides 100% of what the body needs-H2O-without any calories or additives.
Deficiency in any of these nutrients can lead to disease, starvation (or dehydration in the case of water), and subsequent death.
The Importance of Fiber
Fibre, or roughage, is a non-digestible carbohydrate that aids the movement of food through the gut.
Essential Nutrients
The body can manufacture most of the molecules it needs, some essential molecules cannot be made by the body. These molecules are called essential nutrients and must be supplied in the diet, for example lysine and methionine, which are essential amino acids.
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Beyond Nutrients: Flavor and Hydration
Other components of the human diet are not nutrients at all, as they do not perform the functions of producing energy or promoting growth and repair, but are eaten for other purposes. For example, spices and other flavourings help make food more palatable; tea and coffee drinks provide a good source of water and may also contain other valuable substances such as antioxidants.
Dietary Guidelines and Recommendations
An adequate diet is essential for health and education plays a key role in providing people with the knowledge of what constitutes a healthy diet, but as is so often the way with science, the information keeps changing. The information about what we should be eating comes from various sources: in the UK a large amount of data was collected and published by COMA, the Committee on Medical Aspects of Food Policy (1991). This committee has now been disbanded, but its publications still represent a valid source of information about diet. When this course was published (2004), the Scientific Advisory Committee on Nutrition (SACN) advised the Department of Health and the Food Standards Agency (FSA), and the Food Standards Agency produced a guide to choosing a healthy diet, ‘The balance of good health’. Currently (2020) Public Health England produces the Eatwell Guide to visually communicate government recommendations for a healthy diet.
SACN recommends a range of intake levels for all nutrients and energy for males and females throughout life, known as the dietary reference values (DRVs). Because individuals vary in their exact energy requirements, depending on sex, age, occupation and many other factors, often the estimated average requirement (EAR) is given, with the understanding that some individuals need more than this value and others less. Dietary reference values in fact comprise three numbers: the EAR, just discussed, the reference nutrient intake, RNI, and the lower reference nutrient intake, LRNI. These figures replace the old recommended daily amount (RDA), which was felt not to offer sufficient flexibility for individuals’ differing needs. The RNI is set at a level that satisfies the requirements of 97.5% of the population, and the LRNI is set at a level that satisfies the needs of only 2.5% of the population. Thus almost everyone has requirements falling between these two figures.
Individual requirements for nutrients vary considerably depending on factors such as age and sex as you saw above. Other relevant factors are size, metabolic rate and occupation. The situation is further complicated as interactions between components of the diet may alter the efficiency of absorption or utilization of a particular nutrient. The body also has stores of certain nutrients (fat-soluble vitamins, for example) so that variations in daily intake of such nutrients can be accommodated.
Macronutrient Balance: A Closer Look
Fats: Quality Matters
Dietary fat is a terribly misunderstood and mistakenly maligned nutrient. Myths and messages that have persisted since the 1960s warn that “fat is bad.” That dangerous oversimplification has helped launch dozens of largely ineffective diets and the development of thousands of fat-free but calorie-laden foods. It has also helped fuel the twin epidemics of obesity and type 2 diabetes. Trans fats from partially hydrogenated oils are undeniably bad for the cardiovascular system and the rest of the body. Saturated fats from red meat and dairy products increase harmful LDL, but also increase HDL. A moderate intake of saturated fat (under 8% of daily calories) is compatible with a healthy diet, whereas consumption of greater amounts has been associated with cardiovascular disease. Monounsaturated and polyunsaturated fats from vegetable oils, seeds, nuts, whole grains, and fish-especially the polyunsaturated omega-3 fatty acids-are important components of a healthy diet and are also essential for cardiac health. Dietary fat per se is not associated with risk of chronic disease.
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Carbohydrates: Choose Wisely
In the United States, the reduction in the intake of dietary fat from 45% of calories in 1965 to approximately 34% today was accompanied by an increase in the intake of carbohydrates. These extra carbohydrates were largely in the form of highly processed grains. Processing removes fiber, healthful fats, and an array of vitamins, minerals, and phytonutrients, making processed grains such as white flour or white rice nutritionally impoverished compared with whole-grain versions. Consumption of a diet rich in highly processed grains is associated with an increase in triglycerides and a reduction in protective HDL. These adverse responses may be aggravated in the context of insulin resistance, which often develops during pregnancy. The glycemic response refers to the measurable increase in blood sugar after consuming carbohydrates. The greater the postprandial spike in glucose a food generates, the greater that food’s glycemic index. In contrast, whole grains and foods made from whole grains, along with fruits, vegetables, and beans, provide slowly digested carbohydrates that are rich in fiber, vitamins, minerals, and phytonutrients.
Protein: The "Package" Matters
To the metabolic systems engaged in protein production and repair, it is immaterial whether amino acids come from animal or plant protein. However, protein is not consumed in isolation. Instead, it is packaged with a host of other nutrients. The quality and amount of fats, carbohydrates, sodium, and other nutrients in the “protein package” may influence long-term health. Adopting a “flexitarian” approach to protein has long-term health payoffs. Aim for at least half of protein from plants-beans, nuts, seeds, whole grains, fruits, and vegetables. Choose fish, eggs, poultry for most of the rest, with small amounts of red meat and dairy making up the balance.
The Power of Fruits and Vegetables
“Eat more fruits and vegetables” is timeless advice that has the backing of a large body of evidence. Vegetables and fruits provide fiber, slowly digested carbohydrates, vitamins and minerals, and numerous phytonutrients that have been associated with protection against cardiovascular disease, aging-related vision loss due to cataract and macular degeneration, and maintenance of bowel function. The connection between vegetables and fruits and cancer is less well established. Fruits and vegetables should be consumed in abundance, which means a minimum of five servings a day-and more is better. Aim for at least one serving of a dark green leafy vegetable, a yellow or orange fruit or vegetable, a red fruit or vegetable, and a citrus fruit each day.
Beverage Choices: Hydration and Moderation
After water, the two most commonly consumed beverages are tea and coffee. Two problematic beverages are sugar-sweetened drinks (sodas, fruit drinks, juices, sports drinks, etc.) and alcoholic drinks. One 12-ounce can of sugar-sweetened cola delivers 8-10 teaspoons of sugar, approximately 120-150 “empty” calories. Not surprisingly, daily consumption of sugary beverages has been associated with weight gain and increased risk of type 2 diabetes, heart disease, and gout. Alcohol in moderation (no more than one drink a day for women, 1-2 drinks a day for men) has been associated with reduced risks of cardiovascular disease and type 2 diabetes. However, it is possible that a diet rich in folate may attenuate this risk.
Micronutrients: Vitamins and Minerals
An optimal diet generally provides all the vitamins, minerals, and other micronutrients needed for good health. Calcium is important for the maintenance of bone strength. There is mounting evidence that current recommendations for vitamin D (200-600 IU/day, depending on age) are too low, and that 1,000 IU/day provides better protection against fractures and possibly heart disease and some cancers. Excess intake of preformed vitamin A (retinol) has been associated with an increased risk of hip fracture, possibly by competing with vitamin D. Taking an RDA-level multivitamin-multimineral supplement each day that contains folic acid and 1,000 IU of vitamin D provides an inexpensive nutritional safety net.
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The Importance of Weight Management
Body weight sits like a spider at the center of a web of health and disease. Excess weight predisposes an individual to the development of a host of chronic conditions. The higher the body mass index (BMI) > 25 kg/m2, the greater the prevalence of abnormal blood glucose, lipids and blood pressure; hypertension and cardiovascular disease; diabetes; many cancers; gallstones; sleep apnea; complications of pregnancy; infertility; and premature mortality. Maintaining a healthy body weight, or losing weight, is a direct function of calories consumed and expended. Portion control is essential for weight maintenance. The percentage of calories from dietary fat has little relationship with weight maintenance, while low consumption of sugary beverages and trans fats and higher intake of dietary fiber appear to be helpful. Regular exercise and the avoidance of extreme inactivity, such as excessive television watching, are also integral strategies for weight control.
Beyond Individual Nutrients: Dietary Patterns
Although research on nutrients such as fats, carbohydrates, and specific vitamins and minerals has been revealing, it has also generated some dead ends, along with myths and confusion about what constitutes healthy eating. A key reason is because people eat food, not nutrients. Furthermore, humans tend to follow relatively repeatable dietary patterns. One dietary pattern that may harm long-term health is the typical Western diet-rich in red meat, highly processed grains, and sugar, and lacking in fruits, vegetables, whole grains, and fiber.
Evolving Dietary Guidelines: From Pyramid to Plate
The Food Guide Pyramid offered no guidance on grains; it lumped together red meat, poultry, fish, and beans, and it asked us to judge these protein sources by their total fat content. The Food Guide Pyramid promoted drinking three glasses of low-fat milk or eating three servings of other dairy products per day; and made no distinction between types of fat, recommending that fat be consumed “sparingly.” The Food Guide Pyramid was retired in 2005 and replaced with the abstract MyPyramid, which cannot be deciphered without access to the accompanying Web site.
The Healthy Eating Plate, created by nutrition experts at the Harvard T.H. Chan School of Public Health, offers a more science-based approach.
Healthy Eating Plate: A Modern Guide
The Healthy Eating Plate encourages consumers to use healthy oils, and it does not set a maximum on the percentage of calories people should get each day from healthy sources of fat.
- Vegetables: The more veggies - and the greater the variety - the better.
- Fruits
- Whole Grains: Eat a variety of whole grains (like whole-wheat bread, whole-grain pasta, and brown rice).
- Protein Power: Fish, poultry, beans, and nuts are all healthy, versatile protein sources-they can be mixed into salads, and pair well with vegetables on a plate.
- Healthy Plant Oils: Choose healthy vegetable oils like olive, canola, soy, corn, sunflower, peanut, and others, and avoid partially hydrogenated oils, which contain unhealthy trans fats.
- Water, Coffee, Tea: Drink water, tea, or coffee (with little or no sugar). Limit milk/dairy (1-2 servings/day) and juice (1 small glass/day).
The Healthy Eating Plate does not define a certain number of calories or servings per day from each food group. The relative section sizes suggest approximate relative proportions of each of the food groups to include on a healthy plate.
The Mediterranean and DASH Diets: Proven Patterns for Health
Traditional diets developed in countries surrounding the Mediterranean Sea have been linked with lower rates of heart disease and other chronic conditions. Such diets also appear to transplant well to foreign soil. Although there is no single diet that can be called “the” Mediterranean diet, those worthy of the name are high in extra virgin olive oil; high in whole grain foods and fiber; and rich in fruits, vegetables, legumes, and nuts. Small portions of cheese and yogurt are eaten daily; fish is consumed in varying amounts; red meat, poultry, eggs, and sweets are consumed sparingly. Modest amounts of red wine complement meals, and regular physical activity is a part of daily life.
In the 1990s, the National Heart, Lung, and Blood Institute sponsored a randomized, controlled trial called Dietary Approaches to Stop Hypertension (DASH) to see if certain changes in diet could lower blood pressure. The DASH diet emphasized fruits, vegetables, and low-fat dairy foods and limited red meat, saturated fats, and sweets. Compared with an average American diet, the DASH diet lowered participants’ systolic blood pressure by an average of 5.5 mm Hg and diastolic pressure by 3 mm Hg. A low-sodium DASH approach was even more effective; the results were comparable to those from trials of antihypertensive medications.
Practical Advice for Maintaining a Healthy Diet
Fruit and Vegetables
Eating at least 400 g, or five portions, of fruit and vegetables per day reduces the risk of NCDs and helps to ensure an adequate daily intake of dietary fibre. Fruit and vegetable intake can be improved by:
- always including vegetables in meals;
- eating fresh fruit and raw vegetables as snacks;
- eating fresh fruit and vegetables that are in season; and
- eating a variety of fruit and vegetables.
Fats
Reducing the amount of total fat intake to less than 30% of total energy intake helps to prevent unhealthy weight gain in the adult population. Also, the risk of developing NCDs is lowered by:
- reducing saturated fats to less than 10% of total energy intake;
- reducing trans-fats to less than 1% of total energy intake; and
- replacing both saturated fats and trans-fats with unsaturated fats - in particular, with polyunsaturated fats.
Fat intake, especially saturated fat and industrially-produced trans-fat intake, can be reduced by:
- steaming or boiling instead of frying when cooking;
- replacing butter, lard and ghee with oils rich in polyunsaturated fats, such as soybean, canola (rapeseed), corn, safflower and sunflower oils;
- eating reduced-fat dairy foods and lean meats, or trimming visible fat from meat; and
- limiting the consumption of baked and fried foods, and pre-packaged snacks and foods (e.g. doughnuts, cakes, pies, cookies, biscuits and wafers) that contain industrially-produced trans-fats.
Salt, Sodium and Potassium
Most people consume too much sodium through salt (corresponding to consuming an average of 9-12 g of salt per day) and not enough potassium (less than 3.5 g). blood pressure, which in turn increases the risk of heart disease and stroke. Reducing salt intake to the recommended level of less than 5 g per day could prevent 1.7 million deaths each year. People are often unaware of the amount of salt they consume. In many countries, most salt comes from processed foods (e.g. in large amounts (e.g. bread). Salt is also added to foods during cooking (e.g. bouillon, stock cubes, soy sauce and fish sauce) or at the point of consumption (e.g. table salt).
Salt intake can be reduced by:
- limiting the amount of salt and high-sodium condiments (e.g. soy sauce, fish sauce and bouillon) when cooking and preparing foods;
- not having salt or high-sodium sauces on the table;
- limiting the consumption of salty snacks; and
- choosing products with lower sodium content.
Some food manufacturers are reformulating recipes to reduce the sodium content of their products, and people should be encouraged to check nutrition labels to see how much sodium is in a product before purchasing or consuming it.
Potassium can mitigate the negative effects of elevated sodium consumption on blood pressure. Intake of potassium can be increased by consuming fresh fruit and vegetables.
Sugars
In both adults and children, the intake of free sugars should be reduced to less than 10% of total energy intake. A reduction to less than 5% of total energy intake would provide additional health benefits. Consuming free sugars increases the risk of dental caries (tooth decay). Excess calories from foods and drinks high in free sugars also contribute to unhealthy weight gain, which can lead to overweight and obesity. free sugars influence blood pressure and serum lipids, and suggests that a reduction in free sugars intake reduces risk factors for cardiovascular diseases.
Sugars intake can be reduced by:
- limiting the consumption of foods and drinks containing high amounts of sugars, such as sugary snacks, candies and sugar-sweetened beverages (i.e. soft drinks, fruit or vegetable juices and drinks, liquid and powder concentrates, flavoured water, energy and sports drinks, ready‐to‐drink tea, ready‐to‐drink coffee and flavoured milk drinks); and
- eating fresh fruit and raw vegetables as snacks instead of sugary snacks.
Promoting Healthy Diets: A Multi-Sector Approach
Diet evolves over time, being influenced by many social and economic factors that interact in a complex manner to shape individual dietary patterns. healthy foods), individual preferences and beliefs, cultural traditions, and geographical and environmental aspects (including climate change). balanced and healthy diet - requires the involvement of multiple sectors and stakeholders, including government, and the public and private sectors.
Governments have a central role in creating a healthy food environment that enables people to adopt and maintain healthy dietary practices. Effective actions by policy-makers to create a healthy food environment include the following:
- Creating coherence in national policies and investment plans - including trade, food and agricultural policies - to promote a healthy diet and protect public health through:
- increasing incentives for producers and retailers to grow, use and sell fresh fruit and vegetables;
- reducing incentives for the food industry to continue or increase production of processed foods containing high levels of saturated fats, trans-fats, free sugars and salt/sodium;
- encouraging reformulation of food products to reduce the contents of saturated fats, trans-fats, free sugars and salt/sodium, with the goal of eliminating industrially-produced trans-fats;
- implementing the WHO recommendations on the marketing of foods and non-alcoholic beverages to children;
- establishing standards to foster healthy dietary practices through ensuring the availability of healthy, nutritious, safe and affordable foods in pre-schools, schools, other public institutions and the workplace;
- exploring regulatory and voluntary instruments (e.g. marketing regulations and nutrition labelling policies), and economic incentives or disincentives (e.g. the addition of front-of-pack labelling to facilitate consumer understanding; and
- providing nutrition and dietary counselling at primary health-care facilities.
- Promoting appropriate infant and young child feeding practices through:
- implementing the International Code of Marketing of Breast-milk Substitutes and subsequent relevant World Health Assembly resolutions;
- implementing policies and practices to promote protection of working mothers; and
- promoting, protecting and supporting breastfeeding in health services and the community, including through the Baby-friendly Hospital Initiative.