We've all heard the phrase 'the scales don't tell you the truth, they lie'. Well, it's not true. The scales don't lie. The number you can see between your feet is accurate. The same is true of the BMI index. That doesn't lie either. The number you are given is accurate, assuming that you got your height and weight correct.
Tipping the scales
The issue is not whether the scales are right or wrong. The real issue is about how relevant that number is as a standalone figure. How much does weight matter? The answer is, not a lot.
The problem with weight, and BMI, is that they don't tell you the whole story. As guidelines for health both of these numbers are flawed. If we took a cross section of people who all weighed seventy kilos, for example, how different would they look? Probably very different. But why is that? It's because the scales only tell you part of the story. Here's why:
1. Scales don't distinguish between tissues
It's body composition (what our weight is actually made up of) that's important, not weight. Muscle is denser than fat and therefore someone who is lean and muscular will look very different to someone at the same weight with less muscle and more fat. And what about bones? Do sturdier bones make us fatter? No, but they make us heavier.
2. Scales don't account for carb intake
The amount of carbohydrates you consume will significantly affect your weight. Carbs don't make you fat but they are how your body stores fuel in the muscles. The short story is that carbs enter the bloodstream as glucose, which is turn is taken up and stored in the muscles to be used as fuel (glycogen). This muscle glycogen then requires water for it to be used, which makes us store water - clever hey. This storage of fluid makes is heavier. Not fatter. Heavier. And the more muscle mass you have, the bigger this fluctuation will be. This is why ultra low carb diets do wonders for weight loss. But it's weight loss, not fat loss.
3. The scales don't account for water fluctuations
It's pretty obvious that if we're holding more water we'll weigh more. Water is not fat though and lots of things will affect how much water we hold on to. How much we actually drink, the foods we eat (see point two), how heavily and regularly we sweat and our mineral balance are just some of the factors involved in dictating how much water we have present, and thus how much we weigh.
This is the short quick-read version and there are other factors, such as digestive tract health, that will affect weight. But the two key take home points are that losing weight (manipulating fluids) is easy but is not necessarily a true representation of fat lost and it's body composition that's important, not weight.