Kimber Stanhope, PhD, of the University of California Davis, and colleagues reported that, when these types of drinks accounted for at least a quarter of a person’s daily calories over two weeks, there were significant increases in triglycerides, LDL cholesterol, and apolipoprotein B (apoB) concentrations that weren’t seen with glucose.

That finding may have implications for current U.S. dietary guidelines, which suggest limiting added sugar intake to 25% of total energy per day, the researchers said, noting that the American Heart Association recommends an even smaller cap on added sugars at just 5% of daily energy.

To determine the metabolic effects of the various sugars — glucose, fructose, and high-fructose corn syrup — at the 25% intake level, Stanhope and colleagues enrolled 48 patients, ages 18 to 40, who had a body mass index (BMI) of 18 to 35 kg/m².

High-fructose corn syrup is nearly the same as sucrose, or regular table sugar, with its almost 50-50 mix of glucose and fructose.

For the first 3.5 days, patients lived at the research facility and ate a diet that drew 55% of energy from complex carbohydrates, 30% from fat, and 15% from protein.

Then they spent 12 days as outpatients eating their regular diets along with three servings a day of glucose, fructose, or high-fructose corn syrup-sweetened beverages that totaled 25% of daily energy intake.

Finally, patients returned to the lab for another 3.5 days of a strict diet of 25% sugar-sweetened drinks/30% complex carbohydrate, 30% fat, and 15% protein.

During the laboratory phases, the researchers took 24-hour serial blood measurements and fasting blood samples. Overall, they found that the area under the curve (AUC) for 24-hour triglycerides rose significantly over baseline for patients who had fructose and corn syrup-sweetened drinks, by a mean of 4.7 mmol/L and 1.8 mmol/L, respectively (P=0.0032 and P=0.035).

The same increases occurred for fasting LDL cholesterol and apoB concentrations (P=0.0023 and P=0.0005 for fructose; P<0.0001 for both for corn syrup). As well, non-HDL cholesterol and the apoB/apolipoprotein A-1 ratio were similarly increased in these groups over baseline.

None of these parameters changed significantly over baseline for patients whose refreshments were sweetened by glucose.

The researchers did see, however, that fasting triglyceride levels rose with consumption of all three types of sugary drinks, but only significantly so in the glucose group. They also saw a late-evening triglyceride peak between 10 p.m. and midnight across all three groups, which was significant only for fructose and corn syrup — a finding worth additional studies that would look at proatherogenic changes and the sources of triglycerides that contribute to this peak, the researchers said.

Stanhope and colleagues noted that there was an association between BMI and 24-hour triglycerides, but not for any of the other parameters. Nor were there any gender-sugar interactions, they said, although men generally had greater increases in fasting triglycerides, non-HDL cholesterol, and LDL concentrations in response to any sugar.

The researchers concluded that these “established risk factors for coronary heart disease” rise significantly with just two weeks on a diet that draws 25% of its energy from fructose or high fructose corn syrup, even in younger and normal weight people. They noted that while total triglyceride increases were greatest for those on fructose, the fact that LDL and apoB changes tended to be greater with high-fructose corn syrup deserves further study.

Future research should look at whether longer-term consumption of high-fructose corn syrup has further ill effects on metabolism, they said.

The investigators added that the 2010 dietary guidelines, which recommend this 25% of calories from added sugars “may need to be re-evaluated.”

The study was limited because it didn’t specifically investigate consumption of sucrose, even though the added sugar component of the U.S. diet consists of nearly equal amounts of high-fructose corn syrup and sucrose. They noted, however, that they would expect the effects of high-fructose corn syrup to be comparable to those of sucrose because they are chemically similar.