This 2012 review argues the focus public health authorities place on fat and salt restriction is misguided and may be counterproductive if it leads to increased sugar consumption.
Research has linked increased sugar intake to increased disease risk since at least the 1960s, and such research was heavily promoted by T. L. Cleave in the mid-1970s (1). During this same period, however, public health authorities in the United States and other English-speaking Western nations began to recommend population-wide decreases in fat intake, believing fat played a causal role in the development of heart disease (2).
In the 1980s, David Jenkins developed the concept of the glycemic index, a measure of the extent to which a food raises blood glucose levels (3). Sugar was found to have a lower glycemic index than refined starches such as white bread, which led some to recommend that diabetics consume sugar as a healthy carbohydrate to help manage blood sugar levels (4). As a result of these and other forces, sugar intake increased more than 30% between 1970 and 2000 (5). By 2002, the American Heart Association (AHA) had explicitly concluded there was “no definitive evidence” to support the limitation of sugar intake (6).
It is difficult to assess exactly how much sugar the average American consumes, as it is known that surveys relying on self-report underestimate intake by at least 20% (7). With this caveat in mind, economic and survey-based estimates indicate the average American adult consumes between 25 and 45 teaspoons of sugar each day (100 – 180 grams), with one-third of this intake coming from soft drinks; one-third from cakes, cookies, and candies; and the remaining one-third from a variety of other sources (8).
Mechanistically, sugar directly contributes to fatty buildup in organs including the liver and thus contributes to insulin resistance and poor glycemic control as well. Through the effects of insulin, 80% of circulating glucose is cleared out of the blood into skeletal and smooth muscle; only 5% of starch is directed toward liver fat. Fructose, conversely, is taken up directly by the liver after absorption in the intestines, where 50% is converted into glucose and the other 50% is converted into fat. This fatty fraction is either exported by the liver as triglycerides/VLDL or retained in the liver as hepatic fat. This same metabolic process leads to liver cell energy depletion and uric acid production. Higher circulating fat levels lead to fat accumulation in the liver, pancreas, and other organs (9).
At the time of this review (2012), relatively little clinical trial data was available directly linking increased sugar intake to disease progression, or a reduction in sugar intake to disease reversal. A variety of observational data, however, has linked increased intake of sugar or sugar-containing foods to weight gain, diabetes, heart disease, and dental caries. The handful of studies that have failed to show a link between sugar and disease have generally been industry-funded, while independently funded studies have consistently associated increased sugar intake with increased disease risk (10).
As reviewed extensively on CrossFit.com, the evidence linking either saturated fat or salt to increased disease risk is relatively weaker. The Cochrane Collaboration and other groups have found reducing saturated fat intake does not improve cardiovascular mortality and has only an inconsistent effect on the rate of cardiovascular events (11). Recent research has more narrowly argued replacing saturated fats specifically with monounsaturated or polyunsaturated fats is beneficial, but this may be more due to the protective effects of these other fats than any deleterious effects of saturated fat itself (12). Recent reviews of the evidence surrounding salt intake suggest no effect or a limited effect of increased salt intake on heart disease risk, with reduced salt intake potentially increasing overall mortality (13). Low-glycemic-index diets have been consistently linked to reduced mortality, but given a reduction in dietary glycemic index generally involves a variety of dietary changes — i.e., a shift from highly refined foods to vegetables, nuts, and other whole foods — it is impossible to isolate the impact of a change related to glycemic index alone (14).
The authors briefly note anecdotal evidence and previous reviews arguing sugar may have addictive properties and specifically that high-consuming individuals may experience withdrawal symptoms (15). Given the ubiquity of sugar in the Western diet, the effects of abstaining from sugar for extended periods are difficult to study, but these cognitive effects may have contributed to the rapid rise in consumption levels (16).
Since 2009, the AHA has recommended restricting sugar intake to nine teaspoons per day for men, six for women (17). At the intake levels listed above, this represents a two-thirds reduction in sugar intake.
- Saccharine disease: The master of our time; Dietary fat and dietary sugar in relation to ischaemic-heart disease and diabetes; Recent history of coronary disease
- Dietary fat and its relation to heart attacks and strokes; Dietary Goals for the United States
- Glycemic index of foods: A physiological basis for carbohydrate exchange
- Diseases of overnourished societies and the need for dietary change; Sugars and blood glucose control
- The sweetening of the world’s diet
- Sugar and cardiovascular disease: A statement for healthcare professionals from the committee on nutrition of the council on nutrition, physical activity and metabolism of the American Heart Association
- Validity of the 24-hour dietary recall
- The New Zealand sugar (fructose) foundation: time to turn the tide; Usual dietary intakes: Food intakes, US population
- The contribution of naturally labeled C-13 fructose to glucose appearance in humans; Metabolic effects of fructose and the worldwide increase in obesity
- Intake of sugar-sweetened beverages and weight gain: A systematic review; Effects of soft drink consumption on nutrition and health: A systematic review and meta-analysis; Effects of decreasing sugar-sweetened beverage consumption on body weight in adolescents: a randomized, controlled pilot study; Soft drinks, fructose consumption, and the risk of gout in men: Prospective cohort study; Heterogenous effects of fructose on blood lipids in individuals with type 2 diabetes systematic review and meta analysis of experimental trials in humans, etc.
- Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease; Reduced or modified dietary fat for preventing cardiovascular disease; The role of reducing intakes of saturated fat int he prevention of cardiovascular disease: Where does the evidence stand in 2010?
- Major types of dietary fat and risk of coronary heart disease: A pooled analysis of 11 cohort studies; A systematic review of the evidence supporting a causal link between dietary factors and coronary heart disease
- Reduced dietary salt for the prevention of cardiovascular disease
- Low glycemic index or low glycemic load diets for overweight and obesity
- The obesity epidemic: Is glycemic index the key to unlocking a hidden addiction?; Abuse potential of carbohydrates for overweight carbohydrate cravers
- West, Theory of Addiction
- Dietary sugars intake and cardiovascular health: Scientific statement from the American Heart Association, 2009