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Does sugar make you fat?

Eating too much sugar can make you fatter, finds a study.

BMJ Group News

What do we know already?


Sugar has been blamed for causing tooth decay, obesity, heart disease, diabetes, gout, fatty liver disease, some cancers, and hyperactivity. So far, only the link with tooth decay has been firmly established.

Diet is notoriously difficult to study because researchers often have to rely on people reporting what they ate over the past week, month, or year. All sorts of psychological blind spots stop people recalling the details of their eating habits accurately.

Another problem with finding firm links between sugar consumption and disease is that sugar is a very broad term that covers everything from table sugar (sucrose) to starch and pectin (a setting agent in jams and jellies). Studies have tended to define sugar differently, making it difficult to compare results across studies.

To find out if there is a link between sugar consumption and body weight, researchers looked for well-designed studies that only examined a category of sugar called “free sugars”. Free sugars are monosaccharides and disaccharides that are added to foods by the manufacturer, cook, or consumer, plus those naturally present in honey, syrups, and fruit juices. They include sucrose, fructose, glucose, and lactose.

The researchers excluded studies that looked at weight loss or that included people who were ill.

Out of 17,340 studies, they found 68 that met their criteria.

What does the new study say?

Looking at the combined data from the studies (called a meta-analysis), the researchers found that adults who decreased their sugar consumption had an average weight loss of 0.8 kilograms, compared with people who didn’t reduce their sugar consumption. Study durations ranged from 10 weeks to eight months.

In studies where people increased their sugar consumption, there was an average weight gain of 0.75 kilograms, compared with people who didn’t increase their sugar consumption. Most of the studies lasted less than eight weeks.

When the researchers looked at a couple of studies of longer duration (one of 10 weeks and one of six months), they found that increased sugar consumption among adults was associated with an average weight gain of 2.7 kilograms.

In studies where sugars (a type of carbohydrate) were swapped for other carbohydrates, no significant change in weight was seen.

Some of the studies involving children were less conclusive because children found it more difficult than adults to stick to the dietary advice. However, the researchers found that, over a year, children were 55 percent more likely to be overweight if they consumed at least one sugar-sweetened drink a day, compared with children who consumed none or very little.

The researchers guess that the reason people get fat when they eat more sugar could be because it “increases energy consumption to an extent that exceeds energy output and distorts energy balance”. This is a scientist’s way of saying: “sugar makes you eat more”.

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