Exercise causes a variety of hormonal changes that help you mobilize fat stores, but researchers have recently discovered another way exercise helps with fat loss – by its effects on heart tissue. Research shows that during exercise your heart releases hormones known as natriuretic peptides, and these hormones may help you lose body fat.
Natriuretic Hormones and Fat Loss
Researchers at the Sanford-Burnham Medical Research Institute recently discovered that atrial natriuretic peptides released by the heart play a role in fat metabolism. These heart hormones are released by the upper chambers of the heart called the atria when blood pressure rises or the chambers of the heart are stretched. Atrial natriuretic peptides or ANPs also increase during exercise and during periods of calorie restriction. Their primary function is to reduce blood volume and blood pressure by having a diuretic-like effect, meaning they cause you to urinate more. But that’s not the only effect ANPs have on the body. They also have an impact on fat metabolism.
Fat cells have receptors for atrial natriuretic peptides, and when ANPs bind to these receptors, it has an interesting effect. They activate brown fat. Brown fat is a type of fat that’s normally not very energetic in adults. But when brown fat is “turned on,” it converts calories from food into heat so calories from food aren’t stored as white fat, the loose blubbery fat we want less of. Atrial natriuretic peptides released by the heart during exercise have the power to activate dormant brown fat. This helps to keep white fat off our hips and tummies.
Exercise and Fat Loss: The Power of Brown Fat
Scientists have long been searching for a way to activate more metabolically active brown fat. Brown fat is brown because it contains a greater number of mitochondria, tiny organelles that are the energy powerhouse of cells. This “good” fat with its abundance of mitochondria is active during infancy and has the function of keeping a young baby warm. Unfortunately, brown fat shrinks and becomes less active as we age, although researchers believe most adults still retain some, mainly around their neck and clavicle region. This fat can be re-activated under certain circumstances such as exposure to cold.
Studies show that immersing a limb in an ice bath or taking a very cold shower activates brown fat. This makes sense since its purpose is to maintain body temperature. Cold exposure also causes atrial natriuretic peptides to be released by the heart, which may the mechanism by which brown fat is turned on.
Not surprisingly, people who are leaner have higher brown fat stores than those who are overweight or obese, and brown fat may be more active in these naturally lean people. This may explain why some people can eat a large number of calories without gaining weight.
Brown Fat, ANPs and Exercise
Research shows that ANPs increase by up to three-fold during exercise, which helps to ramp up the activity of brown fat. This may be one way that exercise boosts fat loss. If you want to activate brown fat, exercise sounds more pleasant than standing in an ice cold shower.
Other studies looking at brown fat found that exercising mice produce a novel hormone called irisin that converts ordinary white fat to brown fat. The question is whether having more brown fat activity will result in long-term fat loss or whether the fat loss it causes will lead to greater calorie intake to compensate. The body is pretty good at maintaining its set point.
The Bottom Line?
Exercise is not only good for your heart but during exercise, your heart releases hormones that activate fat-burning brown fat. Exposure to cold temperatures may do the same thing.
References:
Vander’s Human Physiology, 11th Ed. McGraw-Hill. pp. 291, 509-10.
N Engl J Med 2009; 360:1500-1508.
Medical News Today. “The Pathway to Losing Fat is Heavily Influenced by a Hormone Produced by the Heart”
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