Just like saving money for a rainy day, our body stores excess calories as fat.
I should mention briefly that insulin plays a significant role in this process, because it facilitates the storage of fat and inhibits its release. Think of insulin as that crazy old cat lady down the street who’s a total pack rat and saves old newspapers and empty peanut butter jars and bits of string, and goes around on garbage day seeing what she can salvage. Insulin has been receiving a lot of attention in recent years for its role in body fat accumulation. It used to be thought that there was a rather simple relationship between dietary fat and body fat (makes sense if you like things to be literal). If we didn’t eat fat, we thought we wouldn’t be fat, though inexplicably many of us (okay, me) got squishy while eating fat-free fig newtons and plain pasta.
It became clear that overall energy balance, or calories in versus calories out, was the most important determinant of body fat gain or loss, but our macronutrient ratio, or the percentages and types of carbs, fat, and protein, was also important. People who gave some attention to the role of insulin in their bodies were often more likely to lose fat and keep it off more effectively. Additionally, current research suggests that eating certain types of dietary fat can actually help keep you lean. Physiology is a head-scratcher sometimes.
Body fat is stored in two places in the body: subcutaneously, or under the skin, and viscerally, or around the internal organs. Visceral fat is much easier to mobilize (lose) than subcutaneous fat, although it increases with age. This age-dependent increase in visceral fat is why body fat calculators should factor in your age: two people with the same skinfold (subcutaneous fat) measurements might have much different overall levels of body fat because of the contribution of visceral fat to the equation. In other words, even if Grandma and little Suzy have the same level of subcutaneous fat, Grandma will likely have more overall body fat because she’ll have much more visceral fat.
Where we store fat is primarily dependent on genetics and hormones. So, if your mother was an apple shape with big boobs and belly, then you’ll likely be too. If mom was a pear with more fat on hips and thighs, then you’ll likely be described, as I was once, as “An hourglass with most of the sand at the bottom”. In general terms, midsection fat gain over the abs, obliques, and lower back is more associated with men, and is referred to as an android (male-pattern, not robot) fat deposition pattern. Lower body fat gain on hips, thighs, and on the tummy below the navel is more associated with women, and is referred to as a gynoid fat deposition pattern. However, there is significant crossover in these patterns, and these patterns can change with age and shifting hormone levels.
When fat is lost, it follows the pattern of fat deposition set out by your genetics and hormones. This means that where you put on fat first is where you lose it last. I think this point is important to emphasize, because it directly contradicts the myth of spot reduction. Barring physical or chemical intervention (e.g. liposuction, hormones), you cannot choose where your body wants to lose or store fat. I think that point is worth some big bold text:
There is no such thing as spot reduction.
All the leg lifts in the word will not change you from J. Lo to Twiggy . It doesn’t matter how hard you try, your body has a plan and it doesn’t like to deviate from it. You may also notice that in the process of losing body fat, fat is lost disproportionately, so that if you’re pear shaped, if you manage to get your hips and thighs skinny enough to do heroin chic modeling, your face will end up looking like it’s been vacuum-sealed in Death Valley and your chest will be flatter than a pool table in Saskatchewan. Competing bodybuilders or fitness competitors about to go on stage look like they’ve just gotten out of POW camps. Some women even get so lean that you can see the top ridge of their breast implants. The effect is minimized on film, but terrifying in person. The negative appearance of very low body fat will also be compounded by age.
What we tend to call “toning” or “definition” simply refers to a loss of body fat so that the muscle underneath may be more clearly seen or felt. There is nothing special about toning or definition. It is not a mystical or special process, one which is restricted to women or a particular workout protocol. It’s a loss of body fat, plain and simple.
Body fat loss also tends to be an imprecise process, in that the body likes to also jettison muscle tissue along with fat (conversely, when muscle mass is gained, some fat mass usually is as well). This varies, however, with how the fat is lost, how much fat is lost, and the starting point of fat loss. If there is a great deal of fat to lose then the percentage of loss which is lean tissue is likely to be less. If fat is being lost by a person who is already at a low body fat, then more muscle relative to fat is consumed.
This loss of muscle is one reason why bodybuilders who wish to compete at extremely low levels of body fat use drugs: it’s hard to get super lean without losing a lot of good stuff too. This is also why it is essential to get sufficient protein and engage in weight training while losing fat, so that the maximum amount of lean muscle tissue is retained. One study which I saw years ago showed that women who were put on equal diets (same amount of calories) lost the same amount of numeric weight (i.e. scale weight in pounds), but the group of women who was weight training wound up with much lower body fat than the sedentary group. Some members of the sedentary dieting group even wound up with more overall body fat as a percentage than they had started with, indicating that there was substantial muscle loss as a result of the dieting.
Thus it is important to stress that weight loss does not equal body fat loss, and vice versa. If being leaner is our goal, we must focus on body fat loss, not on numeric weight.