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Macronutrients: Nutrients that our bodies need in large (“macro”) amounts. These are generally said to include carbohydrates, protein and fat. Each of these provides us with calories and the building blocks for growth and other necessary daily functions.
Carbohydrates: the body’s main source of fuel. They provide the body with necessary glucose, vital for all tissues but especially for the brain, CNS, kidneys and muscles.
Three main types of carbohydrates are fibres, starches and sugar. From the Government of Canada website:
- Fibre is found in beans, bran, fruit, lentils, nuts and seeds, vegetables, and whole grains.
- Starch is found in grains, legumes and vegetables.
- Sugars are found in fruit, juice, milk and some vegetables and are added to many pre-packaged foods such as baked goods, candy, ice cream and soft drinks.
To make healthy carbohydrate choices, choose foods that have more fibre and less sugar; choose more whole grain carbohydrates and less refined carbohydrates. Refined carbohydrates (white bread, pastry, sugary fruit drinks) are easily digested and more easily contribute to weight gain, promote Type II Diabetes and increase the risk of cardiovascular disease.
Choose a variety of whole grain foods for your carbohydrates; bread is not the only carb food! Other options include barley, brown rice, bulgur, oats, quinoa and wild rice. Check out the Canada Food Guide for more ideas.
Instead of …
Wild or brown rice
Yams, sweet potatoes
Konjac or tofu shirataki
White or brown bread
Rye or sourdough
Fruit juice and soda
Lemon water or infusions
Stevia, sugar alternatives
Protein: Like carbohydrates, proteins are a vital macronutrient for building enzymes and tissues, and for growth. The building blocks of proteins are amino acids. While the body can make some amino acids form scratch, some need to be taken in via diet or modified from dietary amino acids. Hence the types of proteins ingested can influence the range of amino acids the body can access. A healthy intake of protein is 1g of protein per kilogram of body weight. Body builders require 2.2 g/per kg.
Animal sources of protein usually contain all the amino acids we need, while other sources such as fruits, vegetables, grains, nuts and seeds may each be missing one or more amino acids. Thus people who eat little animal-based protein need to eat a variety of other protein sources to ensure they are getting all the amino acids they need.
Fats or Lipids: Fat is an important and necessary part of our diet. It forms an important source of essentially fatty acids; fat-soluble vitamins (A, D, E and K) must be digested, absorbed and transported with fats; and fat tissue (adipose tissue) plays an important role in insulation, toxin management, storage and various body functions. Like carbohydrates, however, there are healthier and unhealthier fat choices.
In general, it is better to choose unsaturated over saturated fats. Unsaturated fats are liquid at room temperature and are found mostly in plant-based food such as vegetable oils, nuts and nut oils and seeds. Unsaturated fats can improve cholesterol levels, reduce inflammation and have other positive effects.
There are 2 types of unsaturated fats:
- Monounsaturated fats (e.g. olive oil, canola, peanut oil)
- Polyunsaturated fats (includes fish fats like omega-3 fatty acids)
Even though fatty acids are high calorie, healthy fats are easily utilized for a variety of body functions, as well as ATP production. A healthy diet contains a balance of omega-3 and omega-5 fatty acids; a ratio of 2:1 is ideal. Omega-3 fatty acids help reduce inflammation, and some omega-6 fatty acids tend to promote inflammation. The typical North American diet tends to contain 14 to 25 times more omega-6 fatty acids than omega-3 fatty acids.
For more information on types of fat and examples, see the Harvard School of Public Health “Types of Fat” page.
For more information on omega-3 fats, see their page on “Omega-3 Fatty Acids” page.
Saturated fats are solid at room temperature. They are found mostly in animal fats (meat, eggs, etc.) but can also be found in plant oils (e.g. coconut oil, palm oil).
When trying to avoid saturated fats, some patients may swap them out for refined carbohydrates; instead, you should encourage them to replace saturated fats with good fats, such as monounsaturated and omega-3 polyunsaturated fats. While there is some discussion about the absolute health of saturated fats, it can generally be said that unsaturated fats are healthier than saturated fats.
Trans fats: While a small amount of trans fats can be found naturally in dairy products and beef, much dietary trans fat comes from fried, baked and processed food.
From the Harvard School of Public Health “Trans fats are made by heating liquid vegetable oils in the presence of hydrogen gas and a catalyst, a process called hydrogenation. Partially hydrogenating vegetable oils makes them more stable and less likely to become rancid. This process also converts the oil into a solid, which makes them function as margarine or shortening. Partially hydrogenated oils can withstand repeated heating without breaking down, making them ideal for frying fast foods. For these reasons, partially hydrogenated oils became a mainstay in restaurants and the food industry – for frying, baked goods, and processed snack foods and margarine.”
- Trans fats contribute to cardiovascular inflammation, atherosclerosis and insulin
- resistance. Trans fats are an unhealthy fat choice that create free radical damage in
- the body. They should be avoided.
Micronutrients: nutrients that our bodies need in smaller amounts (“micro”) – nonetheless, these are essential. Micronutrients include vitamins and minerals.
- Vitamins: co-factors for enzymes or intermediates in diverse metabolic processes
- Fat-soluble vitamins (A, D, E, K)
- Water soluble vitamins (B-complex, C)
- Minerals: non-organic elements required for life
- “Macro-minerals” – Ca, PO4, K, S, Na, Cl, Mg
- Trace minerals – Fe, Co, Cu, Zn, Mn, Mb, I, Br, Se
The required micronutrients can usually be gained from a balanced, healthy diet but some individuals may be lacking in micronutrients – either due to constraints in intake (e.g. some vegans), absorption (e.g. celiac) or metabolism/excretion.
Some new diets (e.g. Paleo, gluten-free) may lead to a deficiency of micronutrients, including magnesium.
Glycemic index: How quickly the sugar content of carbohydrates is released into your body. The glycemic index reflects the metabolic burden of food. A high glycemic index increases the risk of diabetes and increases insulin use in diabetic patients
Generally, aim for foods that have lower glycemic index, such as vegetables and whole grains. Additionally, adding fiber and healthy fats to a meal can slow the release of sugar into the body and reduce the glycemic load.
Glycemic load: Absolute load of sugar. Based on blood glucose response and serving size.
- GI x carbohydrate (grams) = GL
- Carbohydrate burden of an amount of food.
Water: While often overlooked, water is of vital importance. 80% of the body’s muscles are water, and it forms 60% of total body mass. While Health Canada offers no specific guidelines on the amount of water needed, intakes should increase in hot environments and during high levels of physical activity. It is also recommended that individuals drink plain or unsweetened sparkling water.
Many patients will seek advice on a “healthy diet”. Often times, this occurs following a diagnosis such as cardiovascular disease. Alternatively, doctors may aim to counsel all of their patients on a healthy diet as part of health promotion.
While encouraging or counseling patients on a healthy diet, it is important to be able to provide a concrete place for patients to start. Below are some basic nutritional aids that can help you counsel your patients in good nutrition.
Canada Food Guide
One place that doctors that doctors can consult for nutritional advice is the Canada Food Guide and the Canadian Food Guide website.
The Canada Food Guide website offers a “My Food Guide” component. This interactive tool customizes the Canada Food Guide for the patient’s needs, recommends various healthy food choices for each of the food groups and recommends physical activity.
The Canada Food Guide also offers a guide that reflects the values, traditions and food choices of First Nations, Inuit and Métis individuals and provides culturally aware nutritional counseling
Plate Method: This method of nutritional counseling focuses on the ratios of various food groups consumed in one meal. Half of a patient’s plate should be non-starchy vegetables and fruit, ¼ grain products and ¼ meat or other protein. A small serving of milk (or an alternative), water and healthy oils/fats should accompany the meal.
The image below is taken from the Government of Canada’s “Build a healthy meal: use the Eat Well Plate”. The site gives more information on the method and recommendations for different groups of food.
Counselling Vegetarian and Vegan Patients
- Vegetarianism or veganism may be a dietary need, a religious choice or a personal choice
- Patients may be uncomfortable bringing up their dietary choices
- Bring up alternative dietary choices in your intake interview and annual check-ups
- Stay informed on health recommendations for alternative dietary choices.
Referrals For Nutrition Counselling
The Canada Food Guide and the Plate Method are basic recommendations for nutrition. Some patients may require more specialized advice. It is important that you keep aware of what specialized diet needs may be required or may help specific conditions that your patients have. Alternately, you may consult with or refer your patient to a nutrition specialist.
Within the Ontario health care system, it is also possible for doctors to refer patients to Registered Dieticians. However, Registered Dieticians are not usually covered by OHIP (though some, such as those that work in Diabetes Education Centres are covered). For private practice dieticians, patients may have to rely on private insurance or pay out-of-pocket.
Another nutrition counseling option is a Nutritionist. While nutritionists are unregulated in Ontario (you therefore cannot refer a patient to them), it is another option that some patients may prefer. As nutritionists are unregulated, it is best to look for individuals with an undergraduate degree in human nutrition or Certified Nutritional Practitioner (CNP) or Registered Holistic Nutritionist (RHN) designation, as those can only be received through a licensed institution.
Both dieticians and nutritionists are trained in food and nutrition and have studied how diet, diet behaviours, nutritional supplements, etc. affect health. Nonetheless, each plays a different role in the health care community. A dietitian, as a registered health professional, works alongside doctors and nurses in hospitals and clinics. They are more likely to be involved in diagnosis of diet-related illnesses and in creating a dietary management plan. Nutritionists may also offer support in this area but more of their work focuses on education, behavioural changes and nutritional guidance for clients.
Note that terminology and coverage for types of nutritional specialists differs across Canada. For example, in Alberta, a “Registered Dietician” and a “Registered Nutritionist” have the same education and training and are both regulated members of the College of Dieticians of Alberta. In New Brunswick, the term is “Dietician-Nutritionist”. Be aware of the options for nutritional specialist in the province in which you are practicing.
Dietary Approaches to Stop Hypertension (DASH) Diet: Dietary approaches offer an alternative to medication in controlling hypertension; some have been shown effective in randomized trials. The DASH eating plan is low in saturated fat, cholesterol and total fat and emphasizes vegetables and fruit, fat-free dairy products and is high in potassium, magnesium and calcium.
- In the original DASH trial patients were randomized to (a) a typical American diet, or (b) a diet rich in fruits and veggies, or (c) a combination diet that had fruits, veggies, plus a reduced fat content. Sodium intake was equal in each diet. At 8 weeks, the fruit & veggie diet reduced SBP by 7.7 mmHg and DBP by 2.8 (compared to the control diet). The combination diet was more effective: 11.4 and 5.5 mmHg). (Appel LJ, Moore TJ, Obarzanek E, et al. The effect of dietary patterns on blood pressure: results from the Dietary Approaches to Stop Hypertension trial. N Engl J Med 1997;336:1117-24) This combination diet has come to be known as the DASH diet.
- Subsequent studies have reduced salt intake with benefits to hypertension control. (Sacks FM, et al. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. NEJM 2001;344:3-10)
- It has also been shown that DASH is effective in virtually removing the 'normal' rise in BP that occurs with age. High protein and low carbohydrate diets have also been compared. (Sacks FM, Campos H. Dietary therapy in hypertension. NEJM 2010;362(22):2102)
- Dietary approaches work most effectively in patients with hypertension, but they may also reduce the risk of developing hypertension (primary prevention). Mediterranean diets appear more effective in reducing body weight than the DASH diet (Sacks FM, Campos H. Dietary therapy in hypertension. NEJM 2010;362(22):2102).
Sacks summarizes his clinical advice as follows:
- Dietary management is appropriate for all patients with hypertension.
- Pre-hypertensive patients (SBP 120 - 139 mm Hg or DBP 80 - 89 mm Hg) should adopt the same dietary changes.
- Drug therapy plays an essential role in treating hypertension. Where lifestyle modification (diet, physical activity, and moderation of alcohol consumption) does not reduce blood pressure below 140/90 mm Hg, drug therapy should be implemented and modified over time given a patient's response.
- However, medication should not supplant dietary management. Both should be considered complementary. The DASH diet is effective in combination with angiotensin-receptor blockers.
- Sodium reduction is highly effective in older patients with hypertension who are taking antihypertensive medicines and in those with resistant hypertension taking several antihypertensive agents.
- We encourage patients to eat poultry, fish, nuts, and legumes instead of red meat; low-fat and non-fat dairy products instead of full-fat dairy products; vegetables and fruit instead of snacks and desserts high in sugars; breads and pastas made from whole grain instead of white flour; fruit itself rather than fruit juice; and polyunsaturated and monounsaturated cooking oils such as olive and peanut oil, rather than butter, or other saturated oils.
The Women's Heart Foundation also provides an example of a DASH approach.
Malnutrition (WHO definition): the cellular imbalance between the supply of nutrients and energy and the body's demand for them to ensure growth, maintenance, and specific functions.
- Malnutrition refers both to inappropriate diet and the medical conditions that result from this, which can be of several kinds: specific dietary deficiencies, general under-nutrition, and also over-nutrition.
The "double burden of malnutrition" refers to regions that simultaneously experience over- and under-nutrition. For specificity, the terms “over nutrition” and “under nutrition” are now used more than “malnutrition”.
Malnutrition may be primary (deriving from an inappropriate diet) or secondary (resulting from another medical condition that affects eating or the absorption of foods, e.g. congenital cardiac disease).
Kwashiorkor: describes a nutritional imbalance, notably a deficit of protein. The child with kwashiorkor often appears miserable; the abdomen may be distended and the legs may show oedema; the skin may have a "flaky paint" appearance and the hair may change colour. Growth is stunted, with the child short for age.
- Means “One-two” because it often happens in children who are still breastfeeding when a younger sibling replaces them; often happens at 1 year.
- More severe effects than marasmus.
Marasmus: involves a deficiency in both proteins and calories but especially calories. Marasmus leads to severe emaciation and muscle wasting; the child is light for their age. Occurs more in younger children.
There are also mixed variants, showing signs of both kwashiorkor and marasmus. The child may show wasting of the upper body combined with edema of the legs.
In addition to simple observation of the child to identify wasting, measuring a child's mid upper-arm circumference (MUAC) offers a quick field assessment of under-nutrition: you can even use your fingers.
More formal assessment involves measuring height and weight. The WHO offers definitions for moderate and severe malnutrition in terms of percentiles or z-scores on their charts of growth standards. Wasting is identified via low weight-for-height and stunting via low height-for-age.
- WHO guidelines on classifying acute malnutrition.
Specific conditions or signs/symptoms related to micronutrient deficiency:
- Anemia (Fe, folate, B12 malabsorption)
- Central nervous system degeneration (water-soluble vitamins, B12)
- Osteoporosis (calcium, Vit. D malabsorption)
- Vitamin D deficiency can lead to osteoporosis, osteomalacia and Rickett’s
- Blindness (Vitamin A malabsorption)
- Scurvy (Vitamin C)
- Pellagra (Dermatitis, Dementia, Diarrhea) (Niacin/Vitamin B3 deficiency)
- Water-soluble vitamin deficiency leads issues with rapidly dividing cell populations leads to: mucocutaneous injury, fatigue, alopecia, dermatitis, neurologic symptoms,
- Zinc deficiency leads to dysgeusia, acrodermatitis, issues with wound healing
- Copper deficiency leads to cytopenias, peripheral neuropathy
Anemia affects large numbers of children and women world-wide: perhaps 45% of pre-school children and over 40% of pregnant women and is common among adolescent girls. Interventions include fortification of flour and supplementation.
Food security refers to having the resources to access a consistently available supply of food, and using the food in an appropriate manner (i.e. access to cooking utensils, stoves, etc.).
Food insecurity refers to the likelihood that a person does not have reliable access to an adequate supply of food, in sufficient quantity and quality. It typically occurs among poor people, may vary seasonally, and is associated with increased weight and obesity.
Food insecurity refers to food of insufficient quality and well as quantity. Refined grains, added sugars, and fats are among the cheapest sources of dietary energy, so are an effective way to save money. They also taste good and are convenient and widely available. However, energy-dense foods tend to be nutrient-poor and have a lower satiating power. This may result in overeating and therefore weight gain.
In contrast, nutrient-dense lean meats, fish, fresh vegetables and fruit generally cost more and they rise in price faster than foods such as soft drinks, sugars and sweets (US Department of Agriculture, 2002).
Even when poorer people are able to purchase fruits, these tend to be nutrient-poor, such as bananas, rather than more expensive berries and nuts.
In Canada, food insecurity has remained fairly stable over the last decade, with about 5% of children and about 8% of adults living in food insecure homes (reference). In total, about 8% of Canadian homes experience food insecurity- but this varies widely by region. Northern Canada is especially vulnerable and Nunavut has the highest food insecurity out of Canadian provinces and territories. In 2011-2012, 36.7% of homes in Nunavut had food insecurity. Additionally, specific household types are more vulnerable for food insecurity. Across Canada, 22.6% of lone-parent families with children <18 reported being food insecure in 2011-2012.
The First Nations Longitudinal Health Survey (FNLHS) found that in 2010 over half (54.2%) of First-Nations homes were food insecure (compared to 9.2% of all Canadians at the time).
Categories of Food Insecurity:
Health Canada rates families, or communities, as
- Food secure (have full access to nutritious foods),
- Moderately food insecure (barriers to food access, with few indications of reduced food intake), or
- Severely food insecure (in addition to ii, they have disrupted eating patterns and reduced food intake)
Several theories have been proposed about the link between food insecurity and obesity.
- Food insecurity leads to consumption of low-cost, energy dense foods that promote weight gain. Healthy foods cost more per calorie than fast foods.
- Food consumption may be cyclical (e.g. when your pay cheque comes in), so people who are food insecure may over-eat when food is available; binge eating is associated with weight gain.
- A confounding argument: Both derive from socioeconomic hardship and the apparent relationship between food insecurity and obesity is due to their joint origins in poverty. Poor people are less likely to exercise properly; less likely to heed recommendations on diet, etc.
- Food insecurity acts as a stressor that triggers psychological and behavioral reactions that include disordered eating, depression and substance abuse which in turn lead to weight gain.
- Obese people apprehensively view themselves as food insecure because they exaggerate the amount they require.
Proposed Solutions To Food Insecurity
- Food banks, soup kitchens: While relied upon by many citizens, these services are stop-gap measures. There are 649 food banks across Canada; they rely on donations so supply can be unpredictable. In 2006, 34% of food banks reported difficulty in meeting demand. They were originally developed as a temporary solution but have proliferated in the absence of a systemic solution to food insecurity. Food banks effectively frame the issue as a food problem and not one of systemic poverty. They may even erode the development of social welfare by placing food supply in the hands of charities, rather than focusing on government policy.
- Community responses: buy local produce programs; collective kitchens; community gardens, etc. These provide subsidized food and educate people. They are intended to be sustainable and to foster mutual support and personal empowerment. They do not, however, overcome the root causes of the problem, and they are generally small-scale ventures.
- Policy options: mainly income-support programs. Governments in Canada seem to acknowledge that food insecurity is a problem, but very few policies address it. Various commissions have proposed policies that have not been adopted. Exceptions include Quebec and Newfoundland, which have both introduced anti-poverty strategies. Quebec's Act to Combat Poverty and Social Exclusion seek to reduce their poverty rates to among the lowest in the world by 2013. It includes a "Programme de subvention en sécurité alimentaire." BC has developed a similar programme.
- The federal government functions mainly to propose standards and prepare documents. They have An Action Plan for Food Security (1998) which proposes priorities for action. They cite poverty reduction strategies, including the Youth Employment Strategy; the National Homelessness Initiative; the National Child Benefit and Old Age Security programmes. Documents include the Pan-Canadian Healthy Living Strategy of 2005.
- The Nutrition North Canada program was launched in 2011 to improve access to foods in remote northern communities.
- There have been difficulties in implementing the recommended strategies; there is inadequate coordination among federal, provincial and municipal governments, and with non-governmental organizations
From PROOF : “There is no comprehensive policy framework in Canada designed to address food insecurity either federally or at the provincial or territorial level. Many provinces have enacted poverty reduction strategies, but household food insecurity has not been an explicit focus of these strategies, nor has their impact on household food insecurity been evaluated. There has been very little written on these policies from a food security perspective, but some research suggests that current strategies in Quebec, which include support for emergency food programs, are insufficient to address food insecurity and disconnected from the desires and needs of food insecure households.”
PROOF is an interdisciplinary research team investigating and publishing on household food insecurity in Canada.
As of 2014, 23.1% of Canadian youth (12-17 y.o.) and 54.0% of Canadian adults (18+) were overweight or obese. Looking specifically at obesity, 6.2% of Canadian youth and 20.2% of adults were obese as of 2014 (source).
Over the last few decades, the obesity rates in Canada have dramatically increased. The Canadian Obesity Epidemic, 1985-1998 (CMAJ, 2002;166:1039) gives maps showing time trends in obesity:
The national prevalence of obesity rose from 5.6% in 1985, to 9.2% in 1990; 13.4% in 1994, 12.7% in 1996 and and 14.8% in 1998 (3.3 million people).
The International Obesity Task Force (IOTF) projects that, by 2025, obesity rates could reach 45-50% in the US, 30-40% in Australia , England and Mauritius, and over 20% in Brazil.
Caring for Overweight and Obsese Patients
Considering these figures, it is certain that you will encounter obese and overweight patients in your practice. While obesity does not guarantee other co-morbidities, it does increase the risk of certain diseases. These include diabetes, osteoarthritis, nonalcoholic fatty liver disease, sleep apnea and others. As such, it is important to keep a dialogue open with your patients about weight and health.
There is considerable stigma faced by individuals who are obese and overweight in Canadian society and patients may feel wary discussing weight with you. Keep discussions supportive and patient-centred.
The counseling approach recommended by the Canadian Obesity Network is the “5As’ of Intervention”.
- Ask: Ask for permission to discuss weight. Weight can be a sensitive issue and patients may be embarrassed or shamed if you bring up weight management without warning or permission. “Can we take a minute to discuss your health and weight?”
- Assess: Assess for obesity-related health risks. Assess also for potential root causes of weight gain (4Ms: mental, mechanical, metabolic and money).
- Assess patient’s Obesity Stage, Obesity Class and Waist Circumference (see below if these terms are unclear)
- Measure patient’s weight and height; don’t rely on self-reporting as it has been shown to lead to systemic under-reporting.
- Advise: Discuss with the patient their obesity-related risks. Obesity risks are more related with Stage than BMI and so the focus of treatment should be on improving health and patient’s wellbeing.
- Interventions may include interventions to sleep, time and stress, dietary changes and low calorie diets, physical activity, psychological treatment, anti-obesity medications, and bariatric surgery.
- Agree: Discuss and agree with your patient on realistic goals. Make a SMART plan to achieve behavioural change.
- Assist: Discuss situations when patient is most likely to fail and strategize a plan. Set a follow-up. Base your counseling then on the stage of change they have reached. Support their effort and re frame failure into a step toward success.
This SIM section is largely based on the 5As of Intervention documents by the Canada Obesity Network.
The Body Mass Index (BMI) offers a general indication of a person's obesity (see critiques of it below, in Additional Information).
The formula is Weight (in Kg) divided by Height2 (measured in metres, and then squared).
If you want to use pounds and inches, the formula is Weight (in pounds) * 703 / Height2 (in inches, squared).
The 703 is a correction factor to make the result equivalent to the metric calculation.
Obesity Class is based on BMI (kg/m2) and is an assessment of the patient’s size:
- Underweight - <18.5 kg/m2
- Normal Weight – 18.6-24.9 kg/m2
- Overweight 25.0-29.9 kg/m2
- Obesity Class I – 30.0-34.9 kg/m2
- Obesity Class II – 35.0-39.9 kg/m2
- Obesity Class III - ≥40.0 kg/m2
- Here are charts showing medians and percentiles to interpret the BMI of children aged 2 to 20 years, for Boys and for Girls.
Obesity Stage is based on the patient’s mental, medical and functional status and is an assessment of the patient’s health.
- Stage 0: No apparent risk factors
- Stage 1: Pre-clinical risk factors
- Stage 2: Established Co-morbidity
- Stage 3: End Organ Damage
- Stage 4: End Stage
Central Obesity/Waist circumference (WC): Excess abdominal fat is an indicator of health risk. Central obesity, defined by waist circumference, may help indicate risk even if the patient is not obese by other standards.
The criteria for central obesity vary based on gender and ethnicity.
The Canada Diabetes Association’s most recent Clinical Practice Guidelines (2013) outline the following gender- and ethnic-specific values for waist circumference.
Country or ethnic group Central obesity as defined by waist circumference. Cm (inches) Men Women European, Sub-Saharan African, Eastern Mediterranean and Middle Eastern (Arab) 94 (37.6) 80 (31.5) South Asian, Chinese, Japanese, South and Central American 90 (36.0) 80 (31.5)
Additional Information: Critiques of BMI
Note that the BMI formula (proposed by Alphonse Quetelet back in 1832) has little logical justification: why not use the cube of height to represent body volume? Indeed, Weight for Height3 is called the Ponderal Index and is used especially for children. However, neither approach is quite right, for studies of scaling suggest a power function between 2 and 3 as optimal. Studies comparing BMI with the Ponderal Index show little improvement with the latter, so BMI is commonly used as being simpler.
The BMI also assumes a fixed fat to muscle ratio, evidently incorrect when one compares an athlete to a sedentary person. Hence the BMI exaggerates obesity for athletes and underestimates it for sedentary people. There are also ethnic differences; for East Asian peoples the upper limit of a healthy BMI is placed around 23, rather than 25, as they have a higher proportion of visceral adipose tissue in the intra-abdominal cavity.
The Canadian Society for Exercise Physiology recommends 150 minutes of aerobic exercise per week (CSEP, 2011). Children should accumulate about 60 minutes' of moderate activity each day. Limit t.v. and video time to a maximum of 2 hours per day.
In 1985, 27% of the population was "physically very active"; in 1991 it was 32% and in 2007, 48% of Canadian adults were "at least moderately active" during their leisure time. 30% participate in organized sports activities. Men are somewhat more active then women.
By age (2005 figures from Statistics Canada):
55 and over
However, the percentage of Canadian adults reaching this recommendation by accumulating at least 30 minutes of moderate-to-vigorous physical activity on at least 5 days per week (as is recommended) is about 5%. (Statistics Canada 2015).
Assessing Physical Activity
In asking a patient about their physical activity, think of "FITT"
- Frequency (how many times per week do you do this?)
- Intensity (how vigorous is the activity?)
- Type (what type of activity?)
- Time, or duration (how long do you spend on it each time?)
The 5A’s of Intervention that we saw before in Obesity Management can also be applied to exercise.
- Ask: "What activities do you enjoy?"
- Assess: "Have you tried to increase your physical activity in the past?" … "What changes did you make?" … "What problems did you experience?" (See FITT questions). While assessing the patient’s physical activity, also establish their readiness for change.
- Advise: (after determining their risk level, and considering any medical contraindication) "Based on ___ , ___ is affecting your health. Regular physical activity for 30 minutes per day, most days of the week, will substantially improve your health. Would you like to discuss what you can do to increase your physical activity?" [Contraindications include AMI, unstable angina, arrythmias, pulmonary embolus, uncontrolled diabetes, etc.]
- Agree: Discuss and agree with your patient on realistic exercise goals. Make a SMART plan to achieve behavioural change .
- Assist: Discuss situations when patient is most likely to fail and strategize a plan. Set a follow-up. Base your counseling then on the stage of change they have reached. Support their effort in increasing activity and re frame failure into a step toward success.
(A good reference is C.S. Ritchie et al. Physical activity assessment and counseling. Nutr Clin Care 2002(May/June);5(3):105-114)
When making an exercise plan with your patients, it is important to discuss barriers that they might have for exercise. Commonly reported barriers include
- Environment (no access to facilities in winter; safety concerns)
- Social (self-conscious; culturally inappropriate; busy at work; no family support; children need to be cared for)
- Attitudes (discouraged after previous failures; unaware of benefits; low self-confidence; 'Just one more thing I have to do'; high expectations)
- Physical (obesity; dislikes sweat & effort; pain; injury)
Help make a plan that accounts for these barriers.
Note that exercise may not have a major role in promoting weight loss (muscle weighs more than fat!), but it appears to help people stay thin if they have lost weight. Higher intensity exercise is more effective at promoting and maintaining weight loss than low intensity exercise.
People who exercise often feel hungrier and eat more. The body aims for homeostasis, so changes in energy balance can increase hormones such as ghrelin which enhance appetite. This seems especially true for women, perhaps as a way to maintain energy stores for reproduction.
It is recommended to have a high carbohydrate snack (e.g. granola bar) after a physical activity to stabilize blood sugar and prevent over eating.
Statistics Canada “Physical activity of Canadian adults: Accelerometer results from the 2007 to 2009 Canadian Health Measures Survey”
If one is looking for a textbook, Advanced Sport Nutrition by Dan Bernadot (RD, PhD, FACSM) is an excellent resource.
Updated January 10, 2018