Does sugar cause cancer?

We all know that consuming too much sugar is not good for our health. Sugar / carbohydrate -rich diets have been linked to diabetes and cardiovascular disease in countless studies. Cancer has also been added relatively recently to the diseases studied in relation to sugar.

Global estimates suggest that around 1 billion people are overweight (a body mass index of 25-30) and approximately 400 million are obese (body mass index >30). According to World Health Organization (WHO) data, in 2018 approximately 18.1 million new cancer cases and 9.6 million cancer-related deaths are estimated worldwide.

The causes of cancer can be grouped into random, mostly age-related mutations (%35), hereditary transmission-familial predisposition (%15), and environmental causes (%50). Environmental causes include smoking, obesity, viruses, bacteria, UV rays, alcohol and chemical carcinogens. Carcinogensare substances and exposures that cause severe genetic damage in cells and trigger mechanisms leading to cancer.

Many studies have examined whether sugar is carcinogenic. Although some have reported positive findings, numerous studies have emphasized that there is no direct link between sugar and cancer.

- Related topic: What are body mass index and obesity, and how are they measured?

We have prepared one of the most current and comprehensive articles in our language on sugar / carbohydrates.

What are sugars / carbohydrates?

Carbohydrates (sugar compounds), like fats and proteins, are among the most important organic nutrients for humans and animals. Their primary purpose is to provide energy. Sugars are abundant organic compounds in our food, consisting of carbon, oxygen and hydrogen. Their structures and names vary according to the number and arrangement of these elements and how humans can use them.

The diagram above shows the building blocks of carbohydrates. Their smallest units are monosaccharides (glucose, fructose and galactose). These combine to form disaccharides (sucrose, maltose, lactose) and polysaccharides (starch, glycogen, cellulose, chitin).

Sugars:

1. Monosaccharides (glucose, fructose, galactose)
2. Disaccharides (sucrose, maltose, lactose)
3. Polysaccharides (starch, non-starch polysaccharides)
4. Sugar alcohols (sorbitol, maltitol, lactitol) and others form various groups

- Related topic: What are starch and fructose, and how does excess sugar become fat?

Studies examining sugar consumption and cancer: the historical process

One review assessing the relationship between sugar consumption and cancer examined 69 studies. The cancers evaluated were breast, pancreatic, prostate, testicular, gynecological, lung, upper digestive tract and bladder cancers. For most sites, too few studies were available to reach a conclusion. The review could not attribute a role to sugar in any cancer. It did find increased breast-cancer risk among heavy consumers of cakes and biscuits known to contain sucrose (table sugar), but these foods also contain substantial fat, so the increase was not attributed to sugar consumption.

The potential for high sucrose intake to increase disease risk has long been studied. Project 259, a study from 1968, found higher serum cholesterol in mice fed a high-sucrose diet than in mice fed a starch-based diet. It was designed to compare whether starch-fed mice had healthier gut flora and therefore a healthier immune system than sucrose-fed mice. The study is also said to have investigated sucrose and cancer risk in mice. However, speculation emerged that the sugar industry prevented publication and instead supported research suggesting dietary fat raised cholesterol more. Indeed, in the 1960-70s the view that fatty foods were more harmful than sugar predominated and remained influential until the 2000s. Today, excessive carbohydrate intake is known to carry as much health risk as excessive fat, and perhaps more.

- Related topic: What are healthy fats?

The effects of sugars and sweeteners in food and drink on cancer formation and spread are being studied increasingly. High fructose intake is thought to trigger non-alcoholic fatty liver disease and the development of a cancer-supporting tumor microenvironment . Fructose has also been shown to increase insulin resistance, inflammation and reactive oxygen species production. Some studies report that sucrose, a disaccharide of glucose+fructose, increases cancer-supporting protein activity, while others show no increase in cancer risk from carbohydrates, particularly fructose. Biochemical and psychological differences may contribute to differing human and animal results. Another confounder may be smoking/tobacco use, a human-specific behavior. Besides being an independent risk factor for many chronic diseases, tobacco also accelerates cancer processes.

The sugar–cancer relationship may be unclear, but a high glycemic index means a rapid rise in blood glucose and insulin release. Heavy consumption of such foods, most of which are sugary, clearly leads to overweight, obesity and diabetes. Obesity is associated with increased risk of many cancers, especially colon and uterine cancer. Pancreatic cancer is an example linked to diabetes. Whether pancreatic cancer results from abnormal glucose metabolism or hyperinsulinemia (excess insulin secretion) predisposes people to it remains debated.

Sugar itself is not established as a cause, but obesity caused by an unbalanced excess of sugar—taking in more energy than we use—is a definite cause of cancer.

Below, we summarize the relationship between carbohydrates, obesity and cancer:

Carbohydrates and obesity

Body weight is determined by genetic, environmental and psychosocial interactions acting through the physiology of energy intake and expenditure. Recent studies have found no consistent relationship between carbohydrates, body weight and the proportion of energy consumed, and have demonstrated the dominance of total energy intake as the main determinant of body weight. Evidence nevertheless shows that specific carbohydrate types, such as sugary drinks, have particular effects on obesity risk. A growing number of systematic reviews have examined low-carbohydrate diets and their effects on weight. In general, they produce at least as much, or more, weight loss than low-fat diets—meaning eating less sugar may be more beneficial than eating less fat. Alternatively, low-carbohydrate diets may reduce insulin concentrations, preventing fat storage and causing weight loss.

Carbohydrates and cancer

Direct links continue to yield mixed results. Earlier systematic reviews propose various claims rather than confirming links to specific cancers. Examples include sucrose and colorectal cancer; lactose and ovarian cancer; fructose and pancreatic cancer; and glycemic load/index and breast, gallbladder, colorectal and endometrial cancers. In contrast, comprehensive meta-analyses have not founda relationship between carbohydrates and gastrointestinal cancer risk. Although cancers have highly variable and diverse causes, a common explanation of carbohydrate involvement includes their metabolic syndrome relationship and its effects on triggering insulin-like growth factors.

Rather than an unproven link between high carbohydrate intake and increased cancer risk, more evidence supports a protective effect of dietary fiber.

Obesity and cancer

Evidence for direct carbohydrate–cancer outcome links is insufficient and limited to a few cancer types. Studies investigating dietary carbohydrates and cancer outcomes have found strong associations between obesity and colon, kidney, gallbladder, pancreatic, endometrial and postmenopausal breast cancers, as well as malignant melanoma, esophageal cancer and leukemia . Increased body mass index has been linked to numerous cancers, including kidney, breast, biliary tract, diffuse B-cell lymphoma, endometrial, thyroid and colorectal cancers and meningioma.

Obesity involves both a marked increase in fat tissue and its remodeling. Both the changes causing obesity and substances released from fat tissue are thought to trigger cancer. Obesity is an independent cancer risk factor.

How much sugar should we consume?

For healthier living, moderation and consuming only as much energy as we expend are beneficial. National and international health organizations recommend limiting dietary sugar and using sugars naturally present in foods, such as fruit sugar and potato starch. Because sugar also harms dental health, WHO recommends that it account for less than %10 of daily energy intake. Its definition of added/free sugars includes sugar in meals, drinks, syrups, honey, fruit juice and juice concentrates, but excludes intrinsic sugars in fruit, vegetables and milk.

The UK Scientific Advisory Committee on Nutrition linked high sugar intake with high-calorie diets, stressed reducing both, and recommended added sugar below %5 of daily energy. The Heart and Stroke Foundation of Canada additionally recommends dietary sugar below %5 against heart disease, stroke, obesity, diabetes, high blood sugar and cancer.

Conclusion

A healthy diet is an important part of personal health. Too much sugar is unhealthy, but current scientific evidence does not establish that sugar causes cancer. Claims that cancer patients are forbidden sugary foods also lack evidence: no such prohibition exists. Excess sugar harms everyone. Within healthy-eating principles, nobody—not just cancer patients—should consume too much. Normal quantities are acceptable. A healthy diet should provide appropriate amounts of fats, proteins and sugars to meet the body's needs.

Related topic:

- What is healthy eating?