Most people think of sugar as “empty calories” — providing only calories. But is it right to consider it so?

It may not be providing any nutritional benefits, but added sugar does plenty of harm. There is a great body of scientific evidence that proves the harmful effects of sugar when the intake is in excess. Most importantly, consumption of excess sugar goes beyond increasing body mass or obesity.

And obesity is not the only reason why people develop diseases/conditions that constitute the metabolic syndrome — diabetes, hypertension, lipid problems, cardiovascular diseases, and non-alcoholic fatty liver disease.

“Obesity is not the cause but only a marker for metabolic dysfunction,” notes a Comment piece published today (February 2) in Nature.

Data provide the proof of this. “Twenty per cent of obese people have normal metabolism,” they note. This is because despite being obese, they do not have insulin resistance. On the other hand, about “40 per cent of normal-weight people develop the diseases that constitute the metabolic syndrome.” The reason: these normal-weight people have insulin resistance.

Insulin is the vital hormone required for storing excess sugar as glycogen in the liver, fat in the adipose tissue and in the muscles. Insulin is also required for breaking down the stored glycogen/fat into glucose when a person is hungry or fasting. This two-way conversion stands compromised in individuals with insulin resistance.

“For the same BMI, Indians have 1.5 times higher insulin resistance compared with Caucasians,” said Dr. V. Balaji, Director and Consultant Diabetologist at the Chennai based Dr. Seshiah Research Institute & Dr. Balaji Diabetic Centre, Chennai.

The evidence

Sugar goes much beyond providing calories, the authors underline. The growing scientific evidence, both epidemiological and mechanistic, very clearly shows that excess sugar induces “all of the diseases associated with the metabolic syndrome.” For instance, excess sugar can “trigger processes that lead to liver toxicity and a host of other chronic diseases,” they warn.

Diabetes is a well known instance. But there are a few more that are less well known. For instance it can raise triglyceride levels. “Trans-fats do not make serum triglycerides,” Dr. Robert H. Lustig, one of the authors of the piece, explained in his mail to this Correspondent. They come from de novo lipogenesis, which means fat that is newly formed in the liver. That is what fructose does.”

Fructose in sugar increases uric acid levels. It can also increase blood pressure in some individuals. Uric acid is a waste product resulting from the metabolism of food. Fructose exerts toxic effects on the liver “similar to those from alcohol.”

Naturally occurring sucrose (sugar) contains 50 per cent of fructose and 50 per cent of glucose.

In a 2010 Editorial in the journal Expert Review of Cardiovascular Therapy Dr. Lustig and Stephanie Nguyen explain the mechanism of how a fructose-rich diet leads to hypertension.

Every small reduction in blood pressure has great benefits. A 2-mm Hg reduction of systolic blood pressure tends to lower mortality from stroke by 10 per cent and from ischemic heart disease by 7 per cent.