So many noticeable things happen when you lose weight — your clothes fit better, you have more energy and you may even feel more confident. But what is actually happening inside your body when the scale ticks down?
Well, quite a lot, as it turns out. And these positive changes might start sooner than you think. In fact, when you lose just 10 pounds — especially if you're overweight — it can kickstart a whole host of bodily shifts toward better health.
To fully understand the biology of weight loss would take the equivalent of 30 semester hours. To save you the trouble of enrolling in university, here's a brief explanation of what's really happening in your body during the early stages of weight loss and the benefits of losing 10 pounds.
Your Fat Cells
You gain weight when you eat more calories than your body needs to support its basic functions — think: respiration and digestion — and energy output, including exercise. Your body converts these excess calories to fat and stores it in your fat cells for later, just in case there's a shortage.
When that shortage doesn't come, and when you continue to exceed your calorie needs, more and more fat is stored in your fat cells, which begin to grow larger and larger. This is the reason your pants seem to get smaller and smaller.
But when you start to lose weight, the opposite happens.
"Dieting produces a condition of negative energy balance, where energy in is less than energy expended. The body must then use stored energy to survive, which primarily comes from our fat cells," Joseph Houmard, PhD, director of the human performance laboratory and professor of kinesiology at East Carolina University, tells LIVESTRONG.com. "With this 'stress' of negative energy balance, hormones in the bloodstream magnify the ability of the fat cells to release stored fat to be used for energy in other tissues."
As this happens, your fat cells shrink — and your pants seem to get bigger and bigger.
This doesn't happen immediately, though. According to authors of a research review published in the Journal of the Academy of Nutrition and Dietetics in March 2014, during the early stage of weight loss the body is primarily burning stored carbohydrates and protein as well as a considerable amount of water.
This early phase lasts several days or weeks, until the body shifts to burning fat for energy. You can expect your fat cells to start whittling away by the time you reach the 10-pound mark, though, which means you'll start noticing changes in the mirror.
Your Blood Pressure
Beyond being able to wear skinny jeans, one of the most important reasons to lose 10 pounds — or more — is heart health.
Being overweight increases the volume of blood your body must circulate through your blood vessels, which increases strain on the arteries, according to the Mayo Clinic. Over time, high blood pressure can lead to a narrowing and hardening of the arteries, affecting their ability to carry fresh, oxygenated blood to the heart. This increases the risk of heart attack, stroke and heart disease.
The good news is that your blood volume decreases quite quickly when you start to lose weight. "The efficiency of weight loss is quite remarkable, with as little as 2 pounds of weight loss producing a one point drop in blood pressure," Houmard says. "Thus, relatively modest amounts of weight loss in the range of 4 to 8 pounds can decrease blood pressure by 3 to 8 points, which is significant in terms of reducing risk for heart disease and other conditions."
Just how weight loss reduces blood pressure is complex. According to Houmard, it has to do with a combination of changing hormones, better kidney function and a decreased strain on the heart.
Other mechanisms behind decreasing blood pressure and blood volume involve terms like "natriuretic peptides" and "renin-angiotensin-aldosterone." But by now you get the basic idea without going into full-on geek mode.
Your Hormone Levels
Hormones are your body's Uber. They carry chemical messages through your bloodstream and tissues that affect things like your metabolism, growth and development, reproduction, sexual function and mood. But excess body fat can affect the normal functioning of hormones, according to Harvard Health Publishing, and the processes they affect that are crucial to health.
A wealth of research, including a study published in the Journal of Clinical Oncology in July 2012, has shown that being overweight or obese can increase a woman's risk of hormone-receptive breast cancer. According to BreastCancer.org, the association isn't fully understood, but it's likely due to increases in hormones, including estrogen, that occur with excess weight.
"Estrogenically active fat is linked with breast cancer. If the fat a woman lost was fat that produced estrogen, then hormonal levels will decrease when that fat is lost. This is why weight loss is recommended to reduce the risk of breast cancer," explains Denise Pickett-Bernard PhD, RDN, LDN, a certified practitioner with the Institute for Functional Medicine.
Losing weight can help normalize hormone levels pretty quickly. In the 2012 Journal of Clinical Oncology study, the women lost 10 percent of their body weight, on average, during the 12-month trial, and markers of several estrogen-like hormones, as well as testosterone, decreased by between 10 and 26 percent.
Interestingly enough, whether the women lost the weight via diet only or by a combination of diet and exercise affected the results. Women who both dieted and engaged in regular exercise had much greater decreases in the potentially risky hormones.
It's not all good news, however. While potentially dangerous levels of some hormones change favorably, other unfavorable hormonal changes may take place, and these can affect your ability to lose 10 pounds and then keep the weight off. "Humans are hardwired to store body fat in case of a famine," Pickett-Bernard says. As explained in a research review published in the International Journal of Obesity in August 2015, our bodies tends to adjust to a calorie deficit in an effort to maintain homeostasis and hold onto fat stores.
To maintain status quo, levels of the appetite-stimulating hormone ghrelin increase, while levels of appetite-suppressing leptin decrease. These hormonal changes can persist even after you've reached your goal, making it difficult to sustain your weight loss.
If you lose 10 pounds with the help of exercise, your body will adapt, according to the Centers for Disease Control and Prevention. At the beginning of a new workout regimen, you're more likely to see fast results in muscle gain and fat loss. Your body is less conditioned, so you have to work harder, and you'll burn more calories than someone who is more conditioned doing the same activity.
The good news is you're getting fitter; the bad news is that you'll have to gradually progress the intensity, duration and/or frequency of your workouts to continue to achieve results.
Being overweight increases your chances of having a sleep disorder, and having a sleep disorder increases your chances of being overweight, say the authors of a March 2013 review in Nature of Science and Sleep. Talk about a double-whammy.
The good news is that losing 10 pounds can improve your sleep along with your risk factors for obesity. In a 2012 study by researchers at Johns Hopkins University School of Medicine, 77 volunteers who were either overweight or obese and who reported a variety of sleep disorders were divided into two intervention groups — a weight-loss diet or a weight-loss diet plus exercise.
- Journal of the Academy of Nutrition and Dietetics: "Time to Correctly Predict the Amount of Weight Loss with Dieting"
- Mayo Clinic: "High Blood Pressure (Hypertension)"
- Journal of Clinical Oncology: "Reduced-Calorie Dietary Weight Loss, Exercise, and Sex Hormones in Postmenopausal Women: Randomized Controlled Trial"
- Breastcancer.org: "Hormone Levels Drop When Obese Women Lose Weight"
- International Journal of Obesity: "Physiological Adaptations to Weight Loss and Factors Favouring Weight Regain"
- CDC: "Physiologic Responses and Long-Term Adaptations to Exercise"
- Michigan Health: "Weighing the Facts: The Tough Truth About Weight Loss"
- Johns Hopkins Medicine: "Losing Weight, Especially in the Belly, Improves Sleep Quality, According to a Johns Hopkins Study"
- Nature of Science and Sleep: "Association Between Sleep Disorders, Obesity, and Exercise: A Review"