Fat Loss Nutrition

Is fruit making you fat?

Aaron Deere is a sports nutritionist, functional medicine consultant and advanced personal trainer. He is based in London.

Fructose, more commonly known as the sugar found in fruit, has been part of the human diet since we started walking upright, and is found in high concentrations in tree and vine fruits, berries, honey, and root vegetables.

It can exist naturally either as a monosaccharide or as a unit of a disaccharide (sucrose). It is roughly 1.73 times as sweet as sucrose and is the sweetest of all the naturally-occurring carbohydrates. Excessive consumption of fructose has been hypothesised to be directly linked to serious health implications including insulin resistance, obesity and, ultimately, metabolic syndrome. So why, having been a part of our diet forever, is fructose suddenly making us fat?

The fructose factor
Firstly, let’s take a look at how the body responds to fructose consumption. It is absorbed from the small intestine much slower than glucose, because glucose has more than one active co-transporter to enter the bloodstream, whereas fructose predominantly relies on GLUT-5 transporters only. Research suggests that doses of up to 12g of pure fructose produced dose-dependent evidence of malabsorption, leading to fluids to be drawn into into the intestines, resulting in stomach ache and diarrhea[1].

Also, while glucose stimulates insulin release from the pancreas, fructose does not, which prohibits it from entering most cells, so it is predominantly retained by the liver. Research has shown hepatic metabolism of fructose results in higher rates of lipogenesis and consequentially increased levels of fatty acid storage within the body[2]. When compared to glucose metabolism, fructose has also been shown to bypass key regulatory feedback steps, with this bypass potentially leading to an increase in fatty acid synthesis, and therefore additional body-fat gain[3].

Research shows that when commercially-produced pure fructose was consumed approximately 45% was used by the body for energy production over a three-to-six hour period. Fructose consumed as glucose (as is typical in natural produce) resulted in up to 66% being used for energy production over the same time frame[4], suggesting why excessive synthetically-produced fructose consumption may result in increased body-fat storage.

Synthetic sweeteners
Fructose is derived commercially from sugar cane and beet, and corn, and its sweetness, combined with low cost of production, has resulted in it being added to foods and drinks to enhance palatability[5]. It is the key ingredient in the synthetically manufactured sweetener high-fructose corn syrup (HFCS), in which hydrolysed corn starch is used as the raw material for production, and glucose molecules are converted into fructose via enzymatic treatment[6].

HFCS is increasingly replacing other forms of sugar in fizzy drinks, as well as many other artificially-sweetened snacks and junk food. The result is that HFCS has become the primary source of dietary fructose for many people, and a parallel rise in levels of obesity suggests a relationship between the two[7].

Limit your exposure
Recommendations for fructose intake vary widely, but international guidelines recommend consuming less than 25% of daily energy intake from sugars. Research suggests that excessive intake of fructose – more than 50g per day – may be linked to health problems, such as metabolic syndrome, obesity, insulin resistance and dyslipidemia (an abnormal amount of lipids in the blood)[8].

Avoiding HFCS entirely can be quite a challenge. Soft drinks and artificially flavoured fruit drinks are obvious sources, but it is now also found in many unexpected places, such as bread, yogurt, cereal, sauces, condiments and preserves. Sticking to a natural, whole food diet and eliminating processed foods will greatly reduce your intake of HFCS, and improve your chances of building a stronger and leaner body.

1, 3  Sun, S. Z., & Empie, M. W. (2012). Fructose metabolism in humans-what isotopic tracer studies tell us. Nutr Metab (Lond), 9(1), 89.
2, 6, 7 Bray, G. A. (2007). How bad is fructose?. The American journal of clinical nutrition, 86(4), 895-896.
4, 8 Johnson, R. J., & Murray, R. (2010). Fructose, exercise, and health. Current sports medicine reports, 9(4), 253-258.
5 Fontvieille, A. M., Faurion, A., Helal, I., Rizkalla, S. W., Falgon, S., Letanoux, M.& Slama, G. (1989). Relative sweetness of fructose compared with sucrose in healthy and diabetic subjects. Diabetes Care, 12(7), 481-486.