A reader recently posted a question asking me to explain how weight loss works. It’s complicated, but in a nutshell, here are the basics:
Ideally, weight loss is about pulling excess body fat out of your fat cells and burning it for fuel. When that happens, your fat cells shrink and you lose pounds and inches.
As I mentioned in a previous blog, when you step on a scale, you’re not just measuring fat. Your total body weight is made up of seven distinct things: 1) muscle 2) bone 3) organs (like your lungs, heart and liver) 4) fluids (including blood) 5) body fat 6) the waste inside your digestive tract you haven’t yet eliminated and 7) glycogen (the form of carbohydrate you sock away in your liver and muscles as a back up fuel).
When the number on the scale changes, it’s mostly due to fluctuations in the amount of water, glycogen (stored carbohydrate) and waste in your body, which shift from hour to hour and day to day. Losing actual body fat takes longer, because the only way to burn excess body fat is to create a calorie deficit, and that can be much trickier than it sounds. To get it right, here’s basically what needs to happen:
1) You need to start eating enough calories, in the right balance, to only support your “ideal” weight. Let’s say you weigh 150 pounds and your ideal weight is 125. That means you’ve been eating enough to support 150 pounds, or even more if you’ve been steadily gaining. For safe, healthful weight loss, you want to eat enough to support all the weight you want to keep, namely your muscle, bone, organ tissue and a smaller amount of body fat. If you eat less than it takes to support your ideal weight, you’ll under-fuel your muscles and organs, and that can cause your body to conserve energy and burn fewer calories, or trigger the loss of muscle mass, which causes your metabolism to slow down. My basic rule of thumb is to never eat less than 10 calories per pound of your ideal weight (unless it’s part of a very short-term “jump start”). So, a person trying to get to 125 pounds should never eat less than 1,250 calories a day. By only eating enough to support your weight goal rather than your current weight, you automatically create a calorie deficit, and for every 3,500 calorie deficit you rack up, you mobilize and burn off one pound of body fat. So, mathematically speaking, the greater the difference between your current weight and your ideal weight, the greater the deficit. That means if two women have the same ideal weight of 125 pounds, a woman who starts out at 175 will lose weight faster than a woman who starts out at 150.
2) Working out increases your deficit. If your deficit is small, let’s say 250 calories a day, you can up it to 500 by burning an extra 250 calories a day through exercise. A daily 500 calorie deficit adds up to 3,500 over a week’s time, to result in a one pound loss of body fat.
3) Research studies have also shown that certain foods can trigger a slight boost in metabolism or result in greater weight loss, even at the same calorie level. We’re also learning more about the role of hormones, but overall, the deficit principle is key.
On weight loss TV shows you’ve probably seen double-digit weekly losses. There are three reasons for this:
1) Most contestants on these shows have 100+ pounds to lose, so again, by starting to eat only the number of calories it takes to support their ideal weight, they instantly create a hefty calorie deficit.
2) These shows typically require several hours of exercise a day, which means the total deficit gets cranked up by a few thousand calories daily.
3) Not all the weight they’re losing is body fat – some, especially in the beginning, is made up of those other factors that affect the number on the scale.
Bottom line: several things influence the “numbers game” that determines fat loss, but one of the most important keys to seeing safe, lasting results is to always eat enough to support the weight you want to be. Unfortunately that means the closer you are to your goal, the smaller the deficit you create, so the longer it takes to lose that next pound. But the good news is doing this the “right” way (e.g. not starving yourself) will keep your metabolism revved up, allow you to feel strong and energized every step of the way, and once you get to your weight goal, you’ll already be eating in a way that allows you to maintain your results.