For most of the second half of the 20th century, dietary fat was the primary suspect in cardiovascular disease. The case for fat was built on plausible biochemistry, large population studies, and the advocacy of physiologist Ancel Keys, who spent decades arguing that saturated fat raised cholesterol and cholesterol caused heart attacks. What was less publicized at the time: the sugar industry paid Harvard researchers to produce papers supporting this narrative while downplaying sugar’s role.

The 2016 publication of those internal Sugar Research Foundation documents, unearthed by UCSF researchers from the archives of deceased Harvard scientists, is one of the better-documented examples of industry interference in nutrition science.

What the Research Now Shows

The 2014 JAMA Internal Medicine study is the anchor study in this area. Quanhe Yang and colleagues at the CDC followed 31,000 US adults for 15 years and tracked added sugar consumption against cardiovascular mortality. People who consumed 17-21% of calories from added sugar had a 38% higher risk of dying from cardiovascular disease compared to those who consumed 8% of calories from sugar. People who consumed 25% or more of calories from sugar, which approximately 10% of American adults do, had more than double the cardiovascular mortality risk.

The effect was independent of age, sex, race, physical activity, body weight, and overall diet quality. It held in normal-weight people as well as overweight people. This is important because it suggests sugar has cardiovascular effects that aren’t mediated entirely through weight.

The Mechanisms

Triglycerides. High sugar consumption, particularly fructose, elevates serum triglycerides. The liver converts excess fructose to fat (de novo lipogenesis), which enters the bloodstream as triglycerides. Elevated triglycerides are an independent risk factor for cardiovascular disease.

HDL cholesterol. Diets high in added sugar tend to lower HDL (“good”) cholesterol. Lower HDL is associated with higher cardiovascular risk.

Blood pressure. Sugar-sweetened beverage consumption is associated with elevated blood pressure in multiple studies. The process is contested, proposed explanations include uric acid production from fructose metabolism (which inhibits nitric oxide synthesis and reduces arterial flexibility), and insulin-mediated sodium retention.

Inflammation. C-reactive protein (CRP) and other inflammatory markers are elevated with high added sugar consumption. Inflammation drives atherosclerosis (the buildup of plaque in arterial walls) and elevated CRP is an early marker of that process.

Endothelial function. Glucose spikes after high-sugar meals impair the function of endothelial cells lining blood vessels. The mechanism involves oxidative stress. Impaired endothelial function is an early marker of cardiovascular disease.

Fat vs. Sugar: What Changed

The fat-causes-heart-disease model was challenged incrementally from the 1990s onward. The Women’s Health Initiative trial, which enrolled 48,000 women and asked them to reduce fat intake substantially, found no reduction in cardiovascular events over 8 years. A 2010 meta-analysis by Siri-Tarino et al. found no association between saturated fat intake and cardiovascular disease when analyzed across multiple cohort studies.

This doesn’t mean dietary fat is irrelevant to heart health. The picture is more nuanced, with trans fats clearly harmful and the effects of saturated fat depending heavily on what it replaces in the diet. But it opened space for reconsidering what the low-fat dietary consensus had left out of the equation, and sugar became a more prominent focus.

The Sugar Research Foundation internal documents published in 2016 showed that this was more than a natural scientific evolution. The industry actively funded research designed to redirect attention from sugar to fat, specifically in the context of heart disease. Two Harvard researchers, Mark Hegsted and Frederick Stare, received the equivalent of $50,000 (in 2016 dollars) from the Sugar Research Foundation to produce a 1967 review paper in the New England Journal of Medicine concluding that fat, not sugar, was the primary dietary driver of heart disease.

The Liquid Sugar Problem

Sweetened beverages show a particularly consistent association with cardiovascular risk, stronger than solid sugar at equivalent doses. The likely explanation is the satiation bypass: liquid calories don’t reduce appetite, so they add to total caloric intake rather than replacing other food.

A 2019 study in Circulation of 80,000 women followed for 34 years found that consuming two or more servings of sweetened beverages per day was associated with a 21% higher risk of coronary heart disease and a 31% higher risk of cardiovascular disease death compared to consuming less than one per month. The effect was concentrated in sweetened beverages specifically, not fruit juice or diet drinks.

Sugar and Heart Disease: Key Numbers

  • 17-21% of calories from added sugar: 38% higher cardiovascular mortality risk (Yang et al., 2014)
  • 25%+ of calories from added sugar: 2x+ cardiovascular mortality risk
  • Approximately 10% of US adults consume 25%+ of calories from sugar
  • Average American: approximately 270 calories per day from added sugar — about 15% of a 1,800-calorie diet
  • 2019 Circulation study: 2+ sweetened beverages daily associated with 31% higher cardiovascular death risk

Explore Further

Sources:

Risk Reduction: What the Evidence Supports

The AHA recommends limiting added sugar to 25g/day for women and 36g/day for men, arriving at these numbers from epidemiological data on the intake levels where cardiovascular risk begins to rise meaningfully. The average American consumes about 77g of added sugar per day (roughly 17% of calories on a 1,800-calorie diet), well above both limits.

Specific interventions with cardiovascular evidence:

Replacing sugar-sweetened beverages with water or unsweetened beverages. This has the most consistent and largest effect size of any single dietary change for reducing sugar intake, and sugar-sweetened beverages have the strongest association with cardiovascular risk of any food category.

Reducing ultra-processed food consumption. Many ultra-processed foods combine sugar with saturated fat, sodium, and refined carbohydrates — a combination that affects multiple cardiovascular risk pathways simultaneously.

Dietary fiber. Diets high in dietary fiber are consistently associated with lower cardiovascular mortality. Fiber slows glucose absorption (reducing post-meal glucose and insulin spikes), feeds gut bacteria that reduce systemic inflammation, and directly reduces LDL cholesterol through bile acid binding.

Why the Evidence Is Hard to Read

The difficulty with a sugar-and-heart-disease paper is that the field went through a decades-long period where the research was actively distorted by industry funding. The 1967 Harvard paper commissioned by the Sugar Research Foundation shaped dietary guidelines for a generation. Teasing apart what the science actually shows from what the industry wanted it to show requires working with primary sources, particularly the Yang et al. 2014 JAMA Internal Medicine study, which used 15 years of follow-up data and was funded by the CDC with no industry involvement.

The most credible position in the current literature: sugar contributes to cardiovascular risk through multiple mechanisms (triglycerides, HDL suppression, inflammation, blood pressure), independently of its contribution to obesity. The effect is real, dose-dependent, and most pronounced for sugar-sweetened beverages.