Liz is a typical 50-year-old woman, fit, 70 kg, 30% body fat. She goes to the gym every day and runs 35 minutes on the treadmill at 10km / h. But, as you often tell me, you can not loose weight. So, what’s going on here: Is it Liz, or is it the universe that conspires against her?
How can you actually lose weight?
Let’s start by looking at the body as an energy store. The body can be divided into two parts. One is the fat mass, the rest of the body is called fat-free mass. It’s mostly water, but there are bone and muscle proteins. Fat contains much more energy (and therefore requires more energy to burn).
Like most adults, Liz wants to lose weight. To do this, she has to go into energy deficit: Energy must be greater than pure energy. How much weight she loses depends on whether she loses fat or fat-free mass.
It takes a much greater energy to lose one kilogram of fat than a kilogram of lean mass. So we need a greater energy deficit per kilogram of weight loss if we are initially thicker.
For most people, it takes an energy deficit of about 27-32 kJ to lose one gram of body weight. If Liz runs on the treadmill for 35 minutes at 10km / h, she has a deficit of about 1500kJ, so she loses only 50g in one session. However, if she does this five times a week for a year, she wants to loose over 12 lbs.
Except, of course, that she does not. After a year she still sticks to 70 kg. Why?
Eat more to balance exercise?
The first possibility is that Liz eats more to make up for the extra movement. Her 35 minutes of treadmill will be completely canceled this evening by a glass and half a merlot.
There is some evidence that people use food to reward themselves for their exercises. A recent analysis has found that post-sport women are particularly vulnerable to fuel. So Liz could unconsciously munch or drink away the energy deficit.
Being less active elsewhere?
A second possibility is that Liz makes up for going to the gym by being less physically active elsewhere. She may fail in front of the television instead of doing housework. Maybe she fidgets even less.
This theory is called the „activitystat“ hypothesis: the idea that we have a set point for the energy expenditure, such as the setpoint of a thermostat. If we increase the physical activity in one area, then there is an automatic balance in another.
So Liz reverses all the good work in the gym by going through the couch potato the rest of the day? We tested this rather depressing theory. Readers will be pleased to know that we found no evidence for the activitystat when sedentary adults started an exercise program. They’ve just boosted the exercise and taken the time out of sleep and watching TV.
Eine Reduzierung des Ruheumsatzes?
Eine der unglücklichen Nebenwirkungen des Abnehmens ist der Ruheumsatz – die Rate, mit der Sie Energie verbrauchen, wenn Sie sitzen und nichts tun – beginnt zu fallen (was bedeutet, dass Sie weniger Energie verbrennen).
Eine neue Studie der Kandidaten auf dem größten Verlierer fand ihre stillstehende metabolische Kinetik wurde niedergedrückt, sechs Jahre nachdem sie verloren und die meisten des Gewichts wiedergewonnen hatte.
So könnte Liz im Prinzip trainieren und ihre Ernährung oder ihr Aktivitätsmuster nicht verändert haben, und trotzdem nicht abnehmen, weil sie einen niedrigeren Ruheumsatz hat. Bei Gewichtsabnahme durch Bewegung (im Gegensatz zur Diät) wird der Ruheumsatz jedoch im Allgemeinen aufrechterhalten.
Vielleicht gewinnst du Muskeln.
Eine sonnigere Aussicht kann sein, dass, während sie nicht Gewicht verloren hat, sie Körperfett verloren hat, und dass Körperfett durch fettfreie Masse ersetzt worden ist. Ein Kilogramm Fett belegt mehr Platz (ca. 1,1 Liter) als ein Kilogramm fettfreie Masse (ca. 0,9 Liter), so dass Liz nicht nur schlanker, sondern auch kleiner wäre.
Wir können berechnen, dass, wenn die Fettmasse vollständig durch fettfreie Masse ersetzt wird, Liz nach 12 Wochen 2,6 kg Körperfett verloren hat und 2,6 kg fettfreie Masse gewonnen hat.
Das klingt gut, aber funktioniert es wirklich so? Eine vernünftige Faustregel ist, dass etwa 75% des Gewichts, das Sie verlieren, Fett sein wird, und der Rest fettfreie Masse. Aber die Dinge können besser laufen, wenn Krafttraining beteiligt ist.
An analysis of previous studies found that the fat-free mass was over 2 kg in overweight and about 1 kg in women, although the weight remained unchanged.
A good test of whether or not you make fat mass mass is just to measure your waist circumference. When it gets smaller while your weight is stable, you are likely to loose fat and gain fat-free mass.
So, what happens to Liz?
Is it food or laziness, or does it loose fat and replace it with fat-free mass? Liz likes this last option, but I do not know. It looks firmer, but the bottle of Merlot is emptier than I thought.
