How Weight Loss Works
Losing weight requires creating a calorie deficit through diet and exercise. But what exactly happens inside your body when you lose weight? This article will explain the science of weight loss and key mechanisms that lead to fat loss and improved health.
Calorie Deficit is Key
The fundamental principle of weight loss is calories in versus calories out. To lose weight, you need to consume fewer calories than you burn each day. This calorie deficit forces your body to break down stored fat to use as energy.
A pound of fat contains about 3,500 calories. So to lose one pound per week, you need a daily calorie deficit of 500 calories. This can be achieved through diet, exercise, or a combination of both. The greater the calorie deficit, the faster the weight loss.
However, women should not consume less than 1200 calories per day, and men no less than 1500 calories, except under medical supervision according to MedlinePlus. Too severe of a calorie restriction slows metabolism and leads to muscle loss and nutrient deficiencies.
Body Fat is Broken Down
During weight loss, the body draws energy from your fat stores. Triglycerides stored in fat cells are broken down into free fatty acids and glycerol. These are released into the bloodstream for use as energy by cells all over the body.
Fatty acids are broken down through beta-oxidation and the citric acid cycle to release energy. The liver also converts fatty acids into ketone bodies which can be used for energy. As your fat stores shrink, so does your weight on the scale.
Muscle Mass Decreases
Weight loss unfortunately also leads to some loss of lean muscle mass. However, the amount depends on several factors. Very low calorie crash diets promote more muscle loss as the body scrambles to find energy sources.
Consuming adequate protein and doing strength training while losing weight can help maintain your muscle mass. Older people tend to lose more muscle since they have less to start with, as explained in this Johns Hopkins Medicine article.
Body Uses Ketones for Fuel
Early in weight loss, your body will start converting more fat into ketone bodies through a process called ketogenesis. Ketogenesis occurs in the liver mitochondria. Ketones can be used as an alternative fuel source when glucose levels get very low due to carb restriction and depleted glycogen stores.
Ketones help preserve muscle mass and function in the absence of adequate glucose from carbohydrates. This metabolic state of increased ketone production is known as ketosis. Nutritional ketosis from a low-carb diet enhances fat burning during weight loss.
Decreased Fat Cell Size
Each fat cell contains a single lipid droplet which stores triglycerides. As the stored lipids get cleared out, the fat cells shrink in size. Although the number of fat cells generally remains constant in adulthood, their volume can vary dramatically.
Losing weight through calorie restriction reduces fat cell size. However, they can rapidly increase in size again when excess calories are consumed, especially sugars. Smaller fat cells have more metabolic benefits for insulin sensitivity and hormone regulation.
Hunger Hormones Change
Weight loss also leads to changes in ghrelin and leptin levels. Ghrelin is a hormone produced in the stomach that stimulates appetite. Leptin is an appetite-regulating hormone secreted by fat cells.
During weight loss, circulating ghrelin levels increase while leptin levels decrease , according to research from the University of Ottawa. These hormonal changes increase appetite. Fighting hunger and sticking to portion control becomes important to continue losing weight.
Improved Insulin Sensitivity
As body fat decreases, especially visceral belly fat, the body becomes more responsive to insulin. This leads to reduced insulin resistance. Obesity promotes insulin resistance which drives weight gain, metabolic syndrome, and type 2 diabetes.
Less fat, particularly around the abdomen, allows insulin to work more effectively. This enables the body to use glucose more efficiently for energy rather than storing excess sugar as fat. Improved insulin sensitivity is a major metabolic benefit of weight loss.
Reduced Inflammation
Excess body fat, especially around the organs, is linked with chronic low-grade inflammation. Fat cells release pro-inflammatory cytokines. This excessive inflammation contributes to insulin resistance, heart disease, and cellular aging.
Weight loss helps reduce systemic inflammation and related health risks . Levels of C-reactive protein, a marker of inflammation, decrease with accompanying fat loss. This helps create a more optimal internal metabolic environment.
Lower Blood Pressure
Overweight and obesity are strongly associated with hypertension. Excess weight puts pressure on blood vessel walls and the heart has to work harder to pump blood. This extra strain raises blood pressure over time.
Losing as little as 5-10% body weight can lower blood pressure significantly in overweight people with hypertension . The result is less pressure on the cardiovascular system and reduced risk of heart attack, stroke, and kidney disease.
Improved Cholesterol Profile
Carrying excess weight often means poor cholesterol numbers. Obesity tends to increase LDL (bad) cholesterol, raise triglycerides, and lower HDL (good) cholesterol. Losing weight can improve all these markers of cardiovascular health.
Even a small amount of weight loss can improve cholesterol numbers. Lower LDL and triglycerides paired with higher HDL reduces buildup of plaque in the arteries. Keeping cholesterol in check helps prevent heart disease and stroke.
Better Physical Functioning
Excess body fat, especially around the midsection and thighs, hinders physical movement and lowers energy levels. Simple activities like walking, bending, and climbing stairs becomes more difficult when obese. Joint pain often worsens due to inflammation.
Losing weight reduces strain on the body, increases ease of movement, and decreases joint pain related to arthritis. Physical functioning and quality of life tend to improve significantly with successful weight loss in obese individuals .
Conclusion
How Weight Loss Works
In summary, weight loss improves health on multiple fronts by: decreasing fat cell size, enhancing insulin sensitivity, reducing inflammation and lowering blood pressure and cholesterol levels. A calorie deficit achieved through diet and exercise sets this beneficial weight loss process in motion.
Though losing weight is challenging, understanding how your body responds biologically provides motivation to keep going. Monitoring your progress with lab tests like cholesterol levels, blood glucose and blood pressure can also help inspire healthy behavior changes, as recommended by Cleveland Clinic.
