What constitutes a healthy diet? Mainstream media and advertisers would like you to think that the answer to this question is complicated and controversial. But science, fortunately, tells us otherwise.
A Conversation about Healthy Eating brings together all the relevant science about healthy eating in one place, and it’s exactly that – a conversation; an informal discussion between a scientist and a friend about their eating habits, keeping the science firmly rooted in everyday life. The conversation moves from topics such as metabolism and digestion to gut bacteria, hormones, neuroscience and the immune system. All of these concepts are explained in accessible terms to help you understand the roles they play in maintaining a healthy diet.
The conversation leads to the conclusion that staying lean and healthy simply requires avoiding the overconsumption of processed foods. While this is, of course, easier said than done, science also provides clear recommendations for how you can adapt your environment and lifestyle to make it possible.
Rather than simply presenting you with the principles of healthy eating, this book will help you to develop a comprehensive understanding of the science behind the principles, including the evolutionary facts that affect the way we eat today. This understanding will allow you to ignore the noise in the media and to move forward with a healthy lifestyle that work for you.
OK, well, before we can get into any of the really interesting stuff, there are a few basic things that you need to understand. I guess we should start with metabolism. Your metabolic systems keep all of the different parts of your body supplied with energy. Because you only eat a few times per day, you need systems that store extra energy after eating and release it slowly between meals.
OK, that sounds simple enough.
Well, there are a few details to consider. First of all, you use two different sources of energy: glucose, which comes from carbohydrates, and fat, which comes from, well, fat. Your muscles – and most of the rest of the cells in your body – are happy to use either but your brain isn’t. Your brain uses only glucose.
Why doesn’t my brain use fat?
Because fat has trouble getting into your brain. Glucose and fat are transported around your body in your blood. Your blood generally moves freely around your body but to enter your brain it has to pass through a filter called the blood-brain barrier. This filter keeps a lot of things out to protect your brain. It turns out that glucose can get through the filter easily but fat can’t.
OK. But if my body and brain are both happy to use glucose, then why don’t I just stick to that and give up on fat altogether?
Good question. The problem is that glucose doesn’t store very well; it’s hard to pack together and it takes up a lot of space. Fat, on the other hand, packs together really well, so it’s perfect for storage.
I see. OK. I guess if most of my body is happy to use fat, and it can be stored more efficiently than glucose, then it makes sense to store most of my energy as fat.
Right. That’s what your fat cells are: storage containers for fat.
But I must need to store at least some glucose to keep my brain going if I don’t eat?
Yes, that’s right, you do store a bit of glucose in your liver, which is your main metabolic organ.
I only store a bit of glucose? That seems risky. What if I don’t eat for a while?
Exactly. If you have to go for a while without eating any glucose, you need a backup plan.
Right. So what is it?
Your liver doesn’t just store glucose, it also makes it whenever your body or brain need it.
Mostly from the waste that is created when you use glucose and fat for energy.
Oh, that’s clever. It’s like recycling.