A new review just published came to the conclusion that “Appetite Rating does not predict energy intake”, meaning: If you ask people how hungry they are, does the response help estimate how many calories they are about to eat? And the answer is: not really.
The paper concludes that
a) appetite ratings are subjective: ‘Very hungry’ or ‘not very hungry’ doesn’t mean the same thing to different people.
b) emotional and behavioural aspects must be taken into consideration: We often eat for reasons other than hunger. We could be bored, sad, upset, stressed or we’re just eating because appealing food is put in front of us or because we don’t want to be rude.
c) more reliable methods to predict energy intake are needed: Maybe. But maybe predicting energy intake isn’t that helpful anyway.
Energy intake means calorie intake. A few months back, I wrote a blog post on why the energy equation (eat less, exercise more) isn’t working very well.
Food is much more than calories. What matters is how we metabolise the food and how it makes us feel. In his book “Always hungry?” Dr David Ludwig explains how what we eat determines how hungry we are, and it appears to be down to the action of insulin.
Insulin is a hormone secreted in response to a carbohydrate containing meal. Most* carbohydrates – whether from sugar or a non-sweet food such as bread – are broken down into glucose molecules, which are then absorbed into the blood stream, thus raising blood glucose levels. The body’s cells use glucose to make energy, and insulin is literally the key to open up the cells for glucose to get in. At the same time, insulin blocks the conversion of energy we previously stored as fat. The body is economical like that: Why use precious stores that are there for a rainy day, if we’ve got perfectly good glucose right here, provided by a meal? Instead of using (‘burning’) body fat, insulin will convert excess glucose from said meal into fat as well and add to our storage.
We eat a high-carbohydrate meal, insulin removes all the resulting glucose from the blood stream and once the cells have used up the glucose that was there, we’ll feel it: We may get tired, grumpy, struggle to concentrate and … get hungry. So, we eat again, likely another high-carb meal that raises insulin levels again and the cycle begins afresh.
No wonder we are always hungry, if insulin is always there to stash away our freshly eaten calories as fat, at the same time making sure that the body fat we already have stays where it is.
A meal that has a low glycaemic load (i. e. a lower carb meal), but contains protein and fat does not raise insulin levels to the same extent. The (reduced) carbohydrates from that meal are also not going to raise blood sugar – and thus insulin – as fast and as high as a high-carbohydrate meal would. That’s because a) a meal that contains protein remains in the stomach for longer than one that doesn’t – thus filling you up sooner and keeping you fuller for longer and b) protein and fat do not trigger insulin secretion. As glucose from the meal doesn’t enter the blood stream all at once, we get a slow and steady supply of energy, rather than a peak and sudden slump. It is those slumps that make us hungry sooner than expected and that give us cravings.
Energy intake – calories – do not come into this at all. What matters is what energy is available to your cells at any given time. Balancing blood sugar ensures a slow and steady supply of glucose and a chance to burn body fat we already have.
* Fibre is also carbohydrate, but we cannot digest it, so it doesn’t raise blood glucose levels.