Overweight and Obesity

*Content has been reviewed by Dr. John Sievenpiper, MD, PhD (Associate Professor, Department of Nutritional Sciences, University of Toronto)

Obesity is a complex, progressive, and relapsing chronic disease characterized by abnormal or excessive body fat accumulation that impairs health (1). 

  • Obesity is a Complex Disease. There are many different risk factors for obesity, such as genetics, dietary habits, level of physical activity, gut (microflora) health, environmental factors, sleep patterns, and mental stress. The amount of body fat and its distribution in the body are more accurate indicators of obesity rather than body weight, which also accounts for muscle and bodily fluids.
  • Diet and Obesity. Research suggests eating too many calories from all sources – sugars, starches, proteins, fats, and alcohol – and not using these calories through normal body functions, movement, and physical activity, can increase the likelihood of storing the excess calories as fat in the body. Other aspects, such as our relationships with food, affordability, culture, and eating behaviours, also play a crucial role in obesity. 
  • Sugars and Obesity. The highest level of scientific evidence has shown that the effect of sugars on obesity is not different from other digestible carbohydrates such as starches, when the total amount of calories consumed remains the same. Overall, body weight is maintained when daily calorie intake is stable, regardless of whether the calories are from carbohydrates, proteins, or fats. 
  • Nutrition in Obesity Management. Long-term diet modifications, such as reducing the frequency or portion size of foods and beverages higher in calories from sugars and fats, and increasing consumption of nutrient-dense foods like fruits and vegetables, can help reduce intake of excess calories, and eventually lead to weight loss. It is important that these modifications are personalized to meet individual values and preferences. 

Obesity is a Complex Disease

Many factors contribute to the risk of obesity including biology (e.g. genetics), diet (e.g. food consumption), individual activity (e.g. physical activity), individual psychology (e.g. emotional stress, depression), activity environment, and societal influences (1,5). 

Having obesity increases risk of several chronic diseases, including diabetes, cardiovascular diseases, musculoskeletal disorders, and some cancers (1). 

Obesity is caused by societal influences, individual psychology and activity, biology, food consumption, food production, activity environment

Body mass index (BMI) is calculated using an individual’s height and weight to determine a numerical value (1). Health complications from excess body fat increase as BMI increases (3). There is an increased risk of impaired health for a BMI of 25.0 to 29.9 kg/m2, and a moderate to severe risk for a BMI greater than 30 kg/m2 (4).  

It is important to note that there are limitations in using only BMI to identify obesity, because body weight, a key determinant of BMI, accounts for not only body fat but also other parts of our body such as muscle and bodily fluids. Excess fat around major organs such as the liver, heart, and kidney (called visceral fat) has been shown to be a direct contributor to metabolic diseases such as heart disease, diabetes, and cancer (15). Obesity Canada recommends that screening for obesity should be performed regularly by measuring BMI and waist circumference (1), and the latter helps identify abdominal obesity, which reflects increased fat around major organs (18-21). 

The Role of Diet in the Development of Obesity

Diet is one factor that may increase risk for obesity. An individual may experience weight gain when more energy (calories) is ingested from all foods and beverages than is expended for normal bodily functions (e.g., breathing, digestion, pumping blood), daily movement and physical activity (4). Fluctuations in energy balance (higher or lower energy intake relative to expenditure) within a meal, day or week are normal and will not necessarily lead to a persistent change in body fat. However, increases in energy intake relative to expenditure (i.e., positive energy balance) over a long period of time may increase the likelihood of the unused calories being stored as fat in the body (6). Data from Statistics Canada also indicate that higher consumption of calories independent of the sources increases risk of obesity (15). It is important to remember that neither excess calorie intake, poor food choices or eating habits is the sole cause for weight gain given the number of factors involved.

Do Sugars Play a Role in the Development of Obesity?

The totality of the best scientific evidence examining the effect of sugars on obesity have shown that: 

  • When the amount of sugars in the diet is either increased or decreased, resulting in a corresponding increase or decrease in daily calorie intake, there is a corresponding change in body weight. However, when calories from sugars are replaced with other sources of calories, leading to a maintenance of total overall calorie intake, there is no change in body weight (5-7).
  • When sweetened beverages are added to a diet, weight gain is often observed. When sweetened beverages are removed, weight loss is observed, demonstrating the impact of the addition and subtraction of calories coming from sweetened beverages on body weight; but when energy intake is controlled there is no change in body weight (7-14).

Obesity rates among children and adults in Canada have continue to rise (please see figure below), according to the Canadian Health Measures Survey which directly measured the height and weight of a nationally representative sample of over 30,000 people (16). Health Canada reports that two out of every three adults in Canada are overweight or obese. The proportion of obese children has nearly tripled in the last 25 years. 

However, trends in per capita (per person) added sugars consumption based on loss-adjusted market availability in Canada plotted against rates of obesity indicate an inverse relationship; as rates of obesity continue to increase, consumption of added sugars has declined. Analyses of the Canadian Community Health Survey (CCHS) 2015 also suggest a reduction in dietary caloric contribution from added sugars among Canadian adults in 2015 as compared to CCHS 2004 (17).

Added sugars consumption has been falling while obesity rates rise in Canada

Figure: Added sugars based on Statistics Canada Availability Data; Obesity rates determined by measured body mass indices from the Canadian Health Measures Survey. 

Nutrition in Obesity Management

Nutrition is not just the food we eat, but also includes our relationships with food, affordability, culture, and eating behaviours. 

From a diet perspective, talking to a registered dietitian may be helpful to determine how to make changes to adopt a healthier dietary pattern that can be sustained. Furthermore, it is quite difficult to manage obesity or lose weight only by “eating less calories”, because of the strong biological mechanisms in the body to act against weight loss, as well as other environmental and social factors (1). Getting enough sleep and incorporating physical activity into daily routines can also help maintain a healthy weight. 

Some suggestions related to diet include: 

  • Selecting nutrient-dense whole foods more often, including whole fruits and vegetables, whole grains, legumes, and lean meats, and less often of other options such as sugar sweetened beverages and fatty meats.
  • Reducing the portion size and/or frequency of higher calorie snacks such as cakes and pastries, chocolate and candies, cookies and granola bars, doughnuts and muffins, ice cream and frozen desserts, French fries, potato chips, nachos and other salty snacks. These foods can be enjoyed as occasional treats rather than every day. 
  • Water is a zero-calorie beverage option to quench thirst.
  • Sugar sweetened beverages can be enjoyed occasionally. In order to reduce the calories from beverages, individuals could:  
    • Mix sweetened carbonated drinks with water 
    • Add lemon wedges or small amounts of 100% fruit juice to water to provide varieties in flavour.
  • Sugars and fats in pre-prepared hot and cold coffee and tea beverages add calories; choosing plain coffee or tea and adding milk and/or a small amount of sugar to suit individual tastes can reduce calories for the day.

Speaking to a physician and a dietitian is encouraged as they can help develop a personalized plan to assess and address the root causes of obesity and provide support for behavioural change (e.g. nutrition and exercise) and other intervention strategies (e.g. mental support, medication, etc.) as needed. Follow the Canadian 24-hour Movement Guidelines to maximize the benefit of physical activity not only for obesity management but for overall health. Aerobic activity (30–60 min) on most days of the week can lead to weight and fat loss, improved risk factors for heart disease, and achieve weight maintenance after weight loss (1). 

A healthy lifestyle includes balanced diet, regular activity

For more information, additional resources include: 
Recent news items include: 

1.    Canadian Adult Obesity Clinical Practice Guidelines. Obesity Canada. https://obesitycanada.ca/guidelines/chapters/
2.    World Health Organization. (2018). Obesity
3.    Global BMI Mortality Collaboration; Di Angelantonio E et al. Body-mass index and all-cause mortality: Individual-participant-data meta-analysis of 239 prospective studies in four continents. Lancet 2016;388:776-86.
4.    World Health Organization. Noncommunicable Diseases: Risk Factors. https://www.who.int/gho/ncd/risk_factors/bmi_text/en/
5.    World Health Organization. Overweight and Obesity. https://www.who.int/en/news-room/fact-sheets/detail/obesity-and-overweight
6.    Centers for Disease Control and Prevention. 2018. Adult Obesity Causes and Consequences.
7.    Te Morenga L et al. Dietary sugars and body weight: systematic review and meta-analyses of randomised controlled trials and cohort studies. BMJ. 2013;346:e7492.
8.    Rippe JM and Angelopoulos TJ. Relationship between added sugars consumption and chronic disease risk factors: current understanding. Nutrients. 2016;8(11):697.
9.    Khan TA and Sievenpiper JL. Controversies about sugars: Results from systematic reviews and meta-analyses on obesity, cardiometabolic disease and diabetes. EJCN. 2016;55(2):25-43.
10.    Ma J et al. Sugar-sweetened beverage consumption is associated with change of visceral adipose tissue over 6 years of follow-up. Circulation. 2016;115.
11.    Malik VS et al. Sugar-sweetened beverages and weight gain in children and adults: a systematic review and meta-analysis. AJCN. 2013;98(4):1084-102.
12.    Hu FB. Resolved: there is sufficient scientific evidence that decreasing sugar-sweetened beverage consumption will reduce the prevalence of obesity and obesity-related diseases. Obes Rev. 2013 Aug;14(8):606-19. 
13.    Kaiser KA et al. Will reducing sugar‐sweetened beverage consumption reduce obesity? Evidence supporting conjecture is strong, but evidence when testing effect is weak. Obesity Reviews. 2013;14(8):620-33.
14.    Trumbo PR, Rivers CR. Systematic review of the evidence for an association between sugar-sweetened beverage consumption and risk of obesity. Nutrition Reviews. 2014;72(9):566-74.
15.    Statistics Canada. 2015. Diet composition and obesity among Canadian adults
16.    Public Health Agency of Canada. Obesity in Canada. June 20, 2011 
17.    Wang Y et al. Canadian Adults with Moderate Intakes of Total Sugars have Greater Intakes of Fibre and Key Micronutrients: Results from the Canadian Community Health Survey 2015 Public Use Microdata File. Nutrients. 2020; 12(4)-1124.
18.    Neeland IJ et al; International Atherosclerosis Society; International Chair on Cardiometabolic Risk Working Group on Visceral Obesity. Visceral and ectopic fat, atherosclerosis, and cardiometabolic disease: a position statement. Lancet Diabetes Endocrinol. 2019 Sep;7(9):715-725. 
19.    Grundy SM, Cleeman JI, Daniels SR, et al. Diagnosis and management of the metabolic syndrome: an American Heart Association/National Heart, Lung, and Blood Institute Scientific Statement. Circulation. 2005;112:2735-52.
20.    International Diabetes Federation. The IDF consensus worldwide definition of metabolic syndrome. Brussels. 2006.
21.    World Health Organization. Definition, Diagnosis, and Classification of Diabetes Mellitus and its Complications: Report of a WHO Consultation. Part I: Diagnosis and Classification of Diabetes Mellitus. Geneva: World Health Organization. 1999.