A Message from the Heart

CHAPTER 9

  

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A Message from the Heart

PART 1

How Obesity Damages the Heart and Blood Vessels

There are three main ways carrying a large amount of excess fat damages your cardiovascular system:

  • Enlarged heart. When you are obese, there is just more of you to furnish with blood supply, and that means increased demands on your heart. One hundred pounds of fat requires an increased blood flow of up to 3 pints (1.5 L) per minute. Not only is there more fatty tissue if you are obese, but there’s more lean tissue, too. All of that tissue must be furnished with a network of capillaries to supply oxygen and nutrients and to take away waste products. Your heart must pump harder to push the blood through the increased amount of blood vessels. One pound of fat requires 1 mile of capillaries to feed it!

    Obesity also increases total body oxygen consumption. Your resting heart rate doesn’t change if you’re obese, so stroke volume—the amount of blood pumped out of the heart with every beat—has to increase to keep up with the body’s demand for oxygen. Your heart has to work harder to increase stroke volume. Working harder can cause your heart to enlarge and, at the same time, pump less effectively. Unlike other muscles in your body, as your heart becomes larger it actually gets weaker. An enlarged heart can eventually result in congestive heart failure. The symptoms are shortness of breath, dizziness, irregular heartbeat, heart palpitations, and fluid retention.

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  • Hypertension. If you’re obese, you’re at high risk for hypertension (high blood pressure). Even moderately obese people have double the risk for hypertension as nonobese people. Having hypertension means the pressure of your blood against the walls of your arteries is too high. Hypertension is sometimes called “the silent killer” because, although it frequently has no symptoms, it can be deadly. It can cause heart disease, atherosclerosis, kidney disease, and other types of damage.

    Why obese people are more at risk for high blood pressure isn’t clearly understood, although it is known that blood pressure increases with weight gain and decreases with weight loss. It may be due to a number of factors, including insulin resistance, overactivity of the sympathetic nervous system, thickened blood vessels, and the increased amount of blood vessels: the more vessels there are, the more pressure that is needed to move the blood.

    Atherosclerosis, or hardening of the arteries, can result when the arterial walls try to defend themselves against the increased force of the blood by becoming stiffer, thicker, and narrower. This can lead to heart attack, stroke, and a host of other complications.

    High blood pressure also causes damage to the heart, because the heart thickens in an effort to pump more vigorously against the higher blood pressure in the vessels. The heart becomes strained and enlarged, and the blood vessels that feed it may be damaged.

  • Abnormal blood lipid levels. Obesity, and particularly abdominal obesity, frequently leads to abnormal levels of blood fats, or lipids. The typical abnormal blood lipid profile is elevated triglycerides, somewhat elevated LDL-cholesterol (the “bad” cholesterol), and lowered HDL-cholesterol (the “good” cholesterol). Although scientists don’t fully understand exactly why this happens, it’s probably because fat tissue produces, amongst other things, free fatty acids. Fatty acids (and other substances) produced by abdominal fat drain into the liver. This stimulates the liver to increase production of triglycerides. High levels of insulin and glucose lead to increased triglyceride production by the liver, too. Lowered levels of HDL-cholesterol happen as a result of the lipolysis (fat burning) of the triglyceride particles.

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PART 2

Heart Attack/Brain Attack

Abnormal blood lipid levels and hypertension both increase the risk of atherosclerosis. In atherosclerosis, cholesterol and other substances create hard, waxy plaques inside your arteries, narrowing them and making it more difficult for blood to get through. READ MORE

Scientists know how atherosclerosis develops, but they’re not entirely sure why it does. It’s thought that plaques may be your body’s attempt to heal the injured inner lining of the arteries. Obesity creates a state of chronic, low-level inflammation throughout the body, and this can injure your arteries. Other disorders associated with obesity can injure arteries as well, such as high blood pressure, high cholesterol, and diabetes. Platelets—blood cells that assist in clotting—clump at the injured site in an attempt to repair it, leading to inflammation. Cholesterol and other substances in your bloodstream accumulate at the site and harden over time.

Because atherosclerosis develops slowly, there may be no symptoms until an artery is so clogged that it can’t deliver adequate blood to your organs or tissues. They become starved of oxygen in a condition called ischemia. Plaques can form in any of the arteries of your body. If atherosclerosis lessens blood flow to your

  • coronary arteries, results may be chest pain (angina), shortness of breath, fatigue

  • brain, consequences can include sudden numbness or weakness in the arms and legs, difficulty speaking, drooping facial muscles

  • arms and legs, walking may become painful

Sometimes plaques rupture. Your body’s immune system attempts to “heal” the injury by forming a clot at the site of the rupture. The clot can cut off blood flow altogether, whether it stays in one place or breaks off and travels through the bloodstream until it gets stuck somewhere. If the clot gets stuck in a

  • coronary artery, the result can be myocardial infarction—a heart attack

  • brain artery (or an artery leading to your brain), the result can be an ischemic stroke, in which blood supply is cut off to portions of your brain

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PART 3

Obesity and Kidney Disease

If you’re obese, you are three to four times more likely to have chronic kidney disease—a gradual, irreversible loss of kidney function. What is the connection between obesity and kidney disease? The kidney’s filtering units are called nephrons. They are very fine blood-filtering tubes, about 1-2 inches long. At one end of the nephron is a capsule that contains a cluster of capillaries called the glomerulus, the kidney's filtration barrier. Tiny capillaries inside the glomerulus do the filtering work of the kidney. READ MORE

These tiny filtering capillaries are very fragile and can be damaged by many of the disorders associated with obesity:

  • Hypertension can injure and even destroy these vulnerable vessels, causing a reduction in both the number of vessels and in their ability to function

  • High insulin levels stimulate the growth of connective (scar) tissue inside the capillary walls

  • Cytokines, signaling molecules secreted in excess by fat tissue (particularly by visceral fat), may also injure capillaries and lead to connective tissue formation

The end result is that connective tissue overtakes the normal tissue that surrounds the healthy glomeruli. Eventually the glomerular capillaries wrinkle, shrink and harden, obstructing blood flow and leaving the glomerulus unable to function.

What’s more, kidney disease causes blood pressure to go up, which further injures the kidneys.

Chronic kidney disease can lead to end-stage kidney disease, the permanent loss of kidney function requiring dialysis or kidney transplantation. LESS
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