The prevalence of obesity was 39.8% among US adults and 18.5% for youth ages 2 to 19 years from 2015 to 2016.1 In 2017, the CDC reported that 29 million individuals (9% of the population) in the US had diabetes mellitus, and this rate has more than doubled since 1999.2,3 The World Health Organization (WHO) estimates that diabetes mellitus caused 1.5 million deaths in 2012 and high blood glucose caused an additional 2.2 million deaths by increasing the risks of cardiovascular and other diseases.4 Evidence supports the suggestion that consumption of excess sugar promotes the development of cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM) both directly and indirectly.
Types of sugar
Sugar can be categorized as either a monosaccharide or disaccharide. The term monosaccharide is derived from the Greek “monos” meaning one or single and “sacchar” meaning sugar. Monosaccharides include glucose, fructose, and galactose and are the simplest form of sugar that the body uses as the primary source of energy. Disaccharides are made of two monosaccharides and include sucrose, lactose, and maltose. Food labels require the identification of added dietary sugar, which includes brown sugar, corn sweetener, corn syrup, dextrose, fructose, glucose, high-fructose corn syrup, honey, lactose, malt syrup, maltose, molasses, raw sugar, and sucrose.5 Each gram of sugar contains 4 calories. Four grams of sugar is equal to 1 teaspoon, and 12 grams of sugar is equal to 1 tablespoon, so food with 20 grams of added sugar has 80 additional calories from that sugar.6,7
The industrial revolution (1750 to 1900) brought about a dramatic increase in sugar consumption as scarcity and cost decreased.8 Products such as cereal, soft drinks, candy, and ice cream became easier to produce and store. This increase paralleled an increase in obesity, T2DM, and CVD.9 Declines in these disease rates were seen only when there were shortages in the availability of sugar such as during World War I. As rates of CVD began to increase disproportionately in the 1950s, scientists began to investigate the possible dietary causes. By the 1960s, there were two divergent theories. John Yudkin, a British physician, physiologist, and nutritionist, identified added sugars as the primary culprit.9 Conversely, Ancel Keys, an American physiologist, hypothesized that an increased intake of saturated fat and cholesterol led to increased rates of CVD.10
The Sugar Research Foundation (SRF) funded most studies during this time period. Industry-sponsored research, much like that sponsored by the tobacco industry, invariably produces results that confirm a lack of harm from the sponsors' products. From an analysis of studies published in the 1950s to 1960s, it was evident that the sugar industry not only paid for but initiated and influenced the research in order to exonerate sugar as a major risk factor of CVD.9
Kearns and colleagues reviewed a case in the Journal of the American Medical Association Internal Medicine from the 1960s where three Harvard researchers were paid by the sugar industry to conduct research related to CVD risk and sugar consumption.9 As a result of this study, a paper published in 1967 reported limited evidence of a link between sugar consumption and heart disease, which contradicted previous studies.9 One scientist paid by the sugar industry, Mark Hegsted, went on to become the head of nutrition at the US Department of Agriculture (USDA), and in 1977 he assisted in drafting the forerunner to the government's dietary guidelines.9 Subsequently, when preliminary findings from animal research funded by the SRF titled “Project 259: Dietary Carbohydrate and Blood Lipids in Germ-Free Rats” led by Dr. W.F.R. Pover at the University of Birmingham, United Kingdom, between 1967 and 1971 suggested a link between increased sugar consumption and both CVD and bladder cancer, the study was defunded.11 Without funding, the study was terminated and the results were not published.10 Internal documents from both studies suggest that the SRF initiated CVD research to protect its market share, and the first literature review published in 1967 did not disclose the sugar industry's role or funding.9
In 2015, the New York Times exposed Coca-Cola's relationship with researchers who were conducting studies aimed at minimizing the effects of sugary drinks on obesity.12 Similarly, the candy trade association funded studies that showed children who eat sweets have healthier body weights when compared with those who eat fewer sweets.10 It was not until 1984 that the New England Journal of Medicine required authors to disclose financial conflicts of interest; however, this transparency does not remove bias, it merely warns the reader about the nature of the bias.13
Evidence suggests that consumption of excess sugar promotes the development of CVD and T2DM. This involves hepatic uptake and metabolism of fructose, which leads to the lipid accumulation in the liver, decreased insulin sensitivity, and increased uric acid levels.14 Consumption of added sugar is associated with the development of dyslipidemia, insulin resistance, fatty liver, hyperuricemia, CVD, and T2DM.14
The prevalence of obesity is increasing in both developed and developing countries. Current estimates suggest that there are approximately 2.1 billion individuals with a body mass index (BMI) categorized as overweight or obese.15 A study published in The Lancet showed approximately a tenfold increase in childhood obesity between 1975 and 2016.16 For adults, overweight is defined as a BMI of 25 mg/kg/m2 to 29 mg/kg/m2 and obesity is defined as a BMI of over 30 mg/kg/m2. For children and adolescents, a BMI of at least 85% is considered overweight, and at least 95% is considered obese. Obesity is a complex, multifactorial disease associated with multiple comorbidities, such as CVD and T2DM.
Evidence from systematic reviews and meta-analyses suggests a direct association between intake of sugar with T2DM, weight gain, overweight, and obesity. Keller and colleagues found a positive association in the majority of reviews between consumption of sugar-sweetened beverages and obesity, especially among overweight children.17 Additional reviews found an association between excess sugar consumption and an increased risk of T2DM, CVD, dental caries, and some cancers.18 Studies such as these have prompted the WHO to recommend a reduced intake of free sugars from birth through adulthood.4
The idea that sugar consumption plays a role in T2DM is not new.19 The food industry argues that obesity and the increase in T2DM are related to energy balance and all consumed calories are equivalent; however, calories consumed from protein and carbohydrates are vastly different based on metabolism. The source from which calories are derived determines how they are metabolized and if they are stored as fat.19
Evidence does suggest that excess sugar consumption is associated with a greater incidence of T2DM. A systematic review conducted by Imamura and colleagues found a substantial increase in cases of new-onset T2DM in individuals who consumed sugar-sweetened beverages habitually over a 10-year span.20 Maki and colleagues found a positive correlation between the development of T2DM and the habitual consumption of sugar-sweetened products when they conducted a randomized clinical trial with 33 subjects using two 6-week treatment periods.21 The WHO's Global Report on Diabetes also concluded that evidence shows an association between high consumption of sugar-sweetened beverages and the risk of developing T2DM.4
Recommendations for intake
Sugar is not an essential nutrient, hence there is no recommended daily allowance.22 Healthy People 2020 goal nutrition and weight status #17.2 is to reduce the consumption of calories from added sugar of the total daily caloric intake to 9.7%.23 This is a decrease from the previous 13.5% in prior recommendations from 2013 to 2016.23 The 2015-2020 Dietary Guidelines for Americans recommend consumption of less than 10% of daily calories from added sugar.24 According to the 2015-2020 Dietary Guidelines for Americans, individuals in the US on average consume 13% or 270 calories per day of added sugar.24 As an example, based on age and gender, if an adult should consume 1,200 calories per day, added sugar should account for less than 120 calories.
A major source of added sugar in the American diet is beverages (soft drinks, fruit drinks, sweetened coffees and teas, energy drinks, alcoholic drinks, and flavored waters). Sugar-sweetened drinks account for 47% of all added sugar consumed by Americans.24 In addition, snack foods such as pastries, desserts, dairy products, candies, jams, syrups, and sweet toppings increase the intake of added sugar dramatically. Sweetened drinks and snack foods together account for 75% of added sugar in the American diet.24 Strategies to decrease sugar intake include choosing drinks with no sugar added, healthy whole foods with no added sugar, and limiting or decreasing portion sizes of sugar-laden foods.
Possible solutions to reduce sugar consumption
Scientific organizations including the WHO, the American Heart Association, the USDA, and the CDC have recommended restrictions related to intake of dietary sugar.2,4,22,25 Effectively addressing the issue does not just happen. It is the result of collective consensus and public investment in interventions that are affordable, cost effective, and based on the best-available science.
Taxation has been proposed as a means of reducing sugar intake and generating revenue for government-funded health programs. Brownell and colleagues suggested that a one-cent excise tax per ounce of any beverage with any caloric sweetener added would generate considerable revenue that could be used to support obesity prevention programs.26 The results of a meta-analysis published by Cabrera Escobar and colleagues suggested that increased prices for sugar-sweetened beverages were related to decreased consumption and the higher the price increase, the greater the reduction in consumption, and there was sufficient evidence for policy makers to consider sugar-sweetened beverage taxation as part of a package of interventions aimed at improving health outcomes and reducing economic burden related to obesity.27
Finding a solution will not be easy. British National Health Service cardiologist Dr. Aseem Malhotra is a founding member and advisor to the campaign group, Action on Sugar. His research suggests that sugar is primarily to blame for heart disease and obesity.28 Malhotra and colleagues argued that the sugar industry has tried to deflect culpability through such means as blaming saturated fat for CVD, co-opting scientists and public health officials, minimizing impact and significant effects by diluting the data, and influencing public opinion through marketing and access.28 Malhotra and colleagues offered the following evidence-based recommendations:
- Education: Emphasize the fact that there is no biological need for and no nutritional value to added sugar.
- Professional sporting events: Ban companies associated with sugary products from sponsoring sporting events. Celebrities and well-known athletes should dissociate themselves from endorsement of sugary products.
- Grocery stores: Ban promotion of sugary foods in grocery stores. Supermarkets should avoid the practice of running end-of-aisle displays of sugary junk foods and drinks.
- Taxation: Extend the tax on sugary drinks to sugary foods.
- Advertising ban: Ban the advertisement of sugary drinks on the internet and TV.
- Food subsidies: Discontinue all government subsidies (for commodity crops, such as sugar). These subsidies distort the market and increase the cost of nonsubsidized crops, making them unaffordable for many individuals.
- Dietary advice: Policy should prevent all dietetic organizations from accepting money or endorsing companies that market processed foods.
- Healthy eating and exercise goals: Healthy eating and physical activity should be separate and independent public health goals. Linking these goals suggests that poor eating can be offset with exercise and the evidence for this approach is weak. The focus needs to be primarily on diet rather than physical activity alone, in order to decrease the deleterious effects of sugar consumption.
- Expert recommendations: In 2015, the WHO published updated, global evidence-informed recommendations on the intake of free sugars to reduce the risk of noncommunicable diseases. They concluded: There is a need for systematic reviews and meta-analyses relating to sugar intake and blood lipid levels.
- Research: Conduct more longer term (longer than 8 weeks) controlled trials of the effect of increasing or decreasing sugar intake on body weight.
- Risk assessment: Assess thresholds above which the consumption of sugar increases the risk of unhealthy weight gain and obesity.
- Behavioral change: Evaluate different behavioral-change approaches to promote the reduction of sugar intake; in particular, the intake of sugar-sweetened beverages, which is identified as a behavioral risk factor contributing to calorie overconsumption, especially among children.29
Further research into dietary patterns contributing to added sugar is warranted. The recommendations related to the upper limits of sugar consumption vary among the medical community, nutritionists, and policy makers. Considering the negative impact that overconsumption of sugar creates, experts in the healthcare and nutrition should come together with policy makers to create legislation that addresses this issue.
After completing a meta-analysis of randomized controlled trials and cohort studies, Morenga and colleagues concluded that a rapid weight gain occurs with an increased intake of dietary sugar and that seems reasonable to conclude that advice relating to sugar intake is a relevant strategy to reduce the high risk of overweight and obesity.30 NPs can play a role in teaching patients how to read food labels and how to identify the type of sugars listed. Patients need to know that their bodies do not need sugar to function and that added sugars contribute zero nutrients and contribute to weight gain and CVD.
There is much to be done in the areas of unbiased research and education for both patients and providers. NPs are responsible for providing patients with the best evidence. Best evidence leads to improved health outcomes and saves medical dollars.
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