Obesity doesn’t just add layers of fat around your thighs and torso. Some of the greatest consequences of poor diet and lack of exercise occur inside your body, out of sight and too often out of mind. We can’t see these health effects, we think, so they must not exist.

A word to the wise: They do. Your body’s biochemistry is complex, and given the relationship between many of your organs and those organs to your physical and mental health, not being able to fit into your jeans may be the least of your problems. Here are five organs that feel the brunt of your obesity.

1. Your Heart

A no-brainer. Excess fat tissue in the body requires oxygen to stay alive. This means your heart recruits more blood vessels to deliver oxygen-rich blood to that tissue. In addition, the more fat that accumulates inside your arteries, the harder those arteries get. Thicker walls allow a narrower space for blood to pass through, so to maintain the same pressure the heart must work harder. Atherosclerosis, the hardening of the artery walls, is 10 times more common in the obese than in healthy people.

There’s no two ways about it; the heart feels the greatest effect from obesity. The muscle itself works harder; the risk for blood clots increases; and the resulting blood circulation throughout the body suffers overall.

2. Your Colon

Researchers haven’t found the connection between obesity and most cancers to be all that strong — except for colon cancer. Among both men and women with obese classifications, colorectal cancers arise with startling frequency. This could be for two main reasons, experts suspect.

The first involves a diet high in processed meats and red meats, a common factor among patients suffering from colon polyps — an early potential sign of colon cancer. The other factor is an elevated level of insulin or insulin-related growth factor in the blood. Why, exactly, these factors influence cancer development remains a mystery. But given the intricate relationship between a person’s digestive system and immune-related disorders — 70 percent of the body’s bacteria live in the gut — the side effects of obesity may explain the link, at least in part.

3. Your Brain

The link between body and mind isn’t new, but the latest science is compelling. A 2010 study found cognitive function showed negative associations with obesity on measures. One hypothesis cites the deteriorating white matter that surrounds nerve fibers in the brain, which send signals around the organ. This white matter sheathing has been found more damaged in the brains of the obese.

“It’s not as though a cable has been cut,” John Gunstad, associate professor at Kent State University and author of the 2010 study, told Science News. “It’s just that its integrity is diminished.” Along the cognitive highways, messages break down and fail to reach their intended targets.

4. Your Skin

It’s easy to forget how much obesity can damage the skin, and contrary to popular opinion, cosmetic blemishes like stretch marks aren’t the only consequence. Hormone changes can cause acanthosis nigricans, a thickening and darkening of the skin; swelling and stretching of the skin can cause redness and irritation, known as stasis dermatitis; and poor vein function can lead to ulcers, found most often in ankles as a result of lacking blood flow.

Maintaining healthy skin is also more than a cosmetic concern. The outer layers of your skin are the foremost barrier to your bloodstream, which means they also serve as the gatekeeper for infectious agents. What begins as a stretched layer of skin may turn into serious illness, all because the body’s mass outmatched the skin’s elasticity.

5. Your Lungs

Like the arteries surrounding your heart, your lungs face great risk in the presence of excess fat. A study published in 2010 showed large amounts of adipose tissue diminishes the organs’ overall capacity for air. This in itself poses significant risk for poor ventilation, which can both exacerbate existing respiratory diseases or produce the same side effects even in the absence of those diseases.

Poor lung function means blood vessels may not be getting enough oxygen. Similarly, obese people face a far greater risk for obstructive sleep apnea than non-obese people, further limiting the oxygen their bodies take in. Problematic enough during the daytime, a failure to breathe at night could turn fatal in a hurry. Researchers are working on a device that delivers tiny electric pulses into the tongue, to release the blockage without waking people up.