Doctors Explain: Why Sugar Makes You Fat and Unhealthy

Tagged in: Diet & Nutrition

by Dr. Bryan Do, D.O. Last Updated: October 30, 2019

why sugar is unhealthy

Our previous article focused on how high carb diets are worse than high fat diets for your health. One of the most common carbohydrates is sugar. This article will explain why sugar or its substitute, high fructose corn syrup (HFCS), makes you fat and unhealthy.

Sugar typically comes in the form of table sugar (sucrose), which is made up of glucose and fructose linked together. In the body, sucrase enzymes in the gut break sugar down into glucose and fructose. In the United States, foods most often substitute with high fructose corn syrup. This is approximately a mix of 43-65% fructose with glucose making up the remainder. The fructose and glucose molecules in high fructose corn syrup are not linked, so it tastes sweeter. Both get absorbed into the bloodstream, but how your body metabolizes fructose is different from how it handles glucose.

How Fructose in Sugar Contributes to Weight Gain

As mentioned, table sugar comprises glucose and fructose. Glucose is a universal form of energy, the easiest source of fuel for all life on earth. Part of this comes from the fact that glucose can be absorbed by all cell types. However, fructose can only be metabolized by the liver. Only the liver has cells that can absorb fructose. Other cells in the body do not have the enzyme. Therefore, all fructose consumed by the body is metabolized by the liver.

This explains why fructose has the negative effects that it does including:

Fructose does not signal for blood sugar regulation

Insulin is the hormone responsible for (among other functions) regulating blood sugar levels. However, fructose does not stimulate insulin release by the pancreas because the pancreas does not absorb fructose. Insulin release is only triggered by glucose.¹

Fructose does not help make you feel full

Leptin is produced by fat cells and helps to regulate energy, calorie burning, and fat storage. It essentially manages long-term food intake to help the body maintain its weight. Sometimes known as the “satiety hormone,” leptin can also help to inhibit hunger. However, leptin secretion is regulated by insulin secretion. As fructose does not stimulate insulin, it has no effect on leptin. This means that fructose has no effect on satiety nor does it reduce food intake.¹

Fructose causes overeating

Known as the “hunger hormone,” ghrelin is responsible for stimulating the appetite. You can think of ghrelin (appetite stimulation) as the counterpart to leptin (appetite inhibition). Ghrelin normally stays high right before meals and decreases after you have eaten. However, studies have found that high fructose intake increases ghrelin levels, which results in overeating.²

Fructose stimulates hunger

Fructose and other sugars have also been shown to disrupt signaling in the hypothalamus. The hypothalamus produces hormones responsible for a variety of functions, from regulating appetite to metabolizing carbs and fats.

Studies have found that fructose can increase neuropeptides in the hypothalamus that stimulate hunger while decreasing chemicals that signal fullness, resulting in overeating.³

Fructose accelerates the aging process

Advanced glycation end products (AGEs) are compounds that form when protein or fat bond with sugar in the bloodstream. While AGEs are most commonly associated with physical signs of aging, the accumulation of these compounds can result in some serious damage to your health. High levels of AGEs have been associated with high blood pressure, heart problems, and chronic diseases.⁴

Studies also found that fructose is seven times likelier to form advanced glycation end products than glucose.⁵ This means that the more fructose you consume, the more AGEs your body will accumulate, accelerating the aging process.

Sugar is addictive

Sugars of all kinds have been shown to be an addictive substance. Studies show that sugar can activate the dopamine and opioid centers of the brain. Opioid centers are generally responsible for providing pain relief, while dopamine influences motivation and feelings of pleasure and reward. Essentially, consuming sugar physically makes you feel good. This may also result in increased cravings for sweets and food in general.⁶

How to Cut Down on Sugar

Cutting down on sugar can be difficult, especially given its prevalence in Western diets and processed foods. Some simple tips for cutting down on your sugar consumption:

Avoid sodas and other sugary drinks (which contain some of the highest amounts of added sugars) in favor of water and herbal teas.
Always check the label for added sugar (fructose, sucrose, etc.) and other common sweeteners, like high fructose corn syrup and evaporated can juice.
Eat slowly to help your body recognize that it is getting full.
Incorporate more fiber into your diet. Fiber increases satiety and is readily found in fruits and vegetables. Opt for whole grains instead of processed grains, which usually have their fiber removed.
Do not use artificial sweeteners as they disrupt the appetite and the body’s natural metabolic regulation.

While sugar in and of itself is not harmful, the fact is, most processed foods contain sugar. This makes it easy to accumulate more sugar in your diet without you consciously knowing.

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About the Author:

Dr. Bryan Do, D.O.

Dr. Bryan Do, D.O. is an osteopathic physician whose research interests include gastroenterology, immunology, and dermatology. He is particularly interested in the role of probiotics in the gut-brain-skin axis and has written many articles on the topic. He graduated from University of California, Los Angeles (UCLA) before graduating from Marian University College of Osteopathic Medicine in Indianapolis, Indiana and becoming a Doctor of Osteopathic Medicine. Osteopathic physicians are taught to take a holistic approach to medicine and to consider mind, body, and spirit when treating a patient. Osteopathic physicians receive training in Osteopathic Manipulative Medicine (OMM) in addition to the standard rigorous medical school curriculum. Both physicians with a Doctor of Osteopathic Medicine (D.O.) degree as well as a Doctor of Medicine (M.D.) can practice medicine.

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