Have you noticed that certain foods make you feel weak or stressed out? Food can have a profound impact on how people think and feel.

This is why diets don’t work unless they fundamentally change your food cravings. If you find yourself returning to junk food after a phase of dieting, it’s not necessarily because you lack willpower – it’s because certain foods really mess with your brain!

Humans have evolved to appreciate three basic flavor categories: sweet, fatty and salty. Sweet foods give you energy; fatty foods give you calories; and finally, salty foods keep you hydrated.

The fact is that humans are hardwired to like these flavors. Food producers know this and have used this fact to their market advantage.

Processed foods such as the hamburgers and french fries from your favorite fast food outlet, chocolate bars and even frozen meals offer a supernormal stimulus, meaning these foods are either sweeter, saltier or fattier (or all three) than non-processed foods. This extra boost makes us crave such foods even more.

When you eat a chocolate bar, for instance, your brain releases dopamine, a neurotransmitter that gives you feelings of pleasure. The more chocolate you eat, the more your body craves the effect of dopamine; and this feedback loop makes you want to eat more chocolate in the future.

Yet food doesn’t just scramble your brain, convincing you that another cheeseburger can’t be all that bad. It also affects your immune system, potentially causing inflammation.

Inflammation in the body usually happens as a normal response to an injury or illness, but chronic inflammation is different. Chronic inflammation occurs when your immune system gets confused and your body starts attacking itself, as it can’t differentiate between “you” and a foreign invader, such as a virus.

A lot of processed food today contains chemical compounds that can be difficult for your immune system to process. Such chemicals can stress your body, leading to chronic inflammation and even serious illness.

Food can actually change how your hormones work. Your body’s hormones are supposed to keep your system in balance, but certain foods can throw your body’s system off balance.

Insulin, which controls the body’s blood sugar levels, is the most important hormone associated with food. Chronically high levels of blood sugar are harmful, and can cause diabetes. Insulin is supposed to prevent this by telling your body to store extra sugar as glycogen, to be used later when your body needs it.

If you eat too much sugar, however, your glycogen reserves fill up and your body stores the sugar instead as triglycerides, or fat. When this happens, a hormone called leptin is thrown off balance.

Leptin tells your brain to stop eating when you’re full. When you consume too much sugar, your brain can’t properly read your leptin levels. You could develop leptin resistance and overeat, because you won’t feel full when you should.

What’s more, if your brain can’t properly detect leptin levels, it may think you’re too skinny, further pushing your body to produce more fat.

It is actually harmful for your cells to be stuffed with too much energy from sugars, so the cells protect themselves by becoming insulin resistant. Your brain responds to this event however by releasing even more insulin. This excess causes you to feel dizzy (as if you haven’t eaten), as your body thinks it needs more energy!

The food you eat also affects the health of your gut. Comprising some 80 percent of your immune system, the gut is where food is broken down into its component nutrients.

The gut protects the body by acting as a barrier, catching harmful substances you ingest before they make it “inside” to affect your immune system. Once bad stuff gets inside, however, it is much harder for your immune system to cope.

Most people know it’s unhealthy to eat too much sugar or drink too much alcohol. But other foods that may seem more benign can also be bad for your health.

Try to keep all grains and legumes out of your diet, even such “healthy” options as quinoa or whole-grain (or brown) rice. While grains are nutritious, they are not as nutritious as fruits and vegetables. They have a higher calorie content, too. When you eat grains, you may eat fewer fruits and vegetables because grains can fill you up so easily!

Your body can’t use all the nutrients in grains, either. Grains contain a lot of phytate, an acid that helps plants store phosphorous (to help them grow). But phytate can also bind with essential minerals such as zinc, which keeps your body from absorbing them – potentially leading to deficiencies.

Legumes such as beans, peas, lentils and peanuts contain a lot of phytate as well.

Even soy products such as tofu aren’t great for human consumption. Soy contains isoflavones, which are a type of phytoestrogen. Your body treats phytoestrogens as it does female reproductive hormones, which in excess can be harmful. For men, it can lead to a testosterone imbalance; for women, it can speed up the growth of breast cancer cells.

It’s also good to avoid dairy products and seed oils. Milk doesn’t just include useful calcium and calories, but also may include naturally occurring growth hormones – good for baby calves, but unhealthy for humans.

Seed oils, such as sunflower oil or sesame oil, have high levels of omega-6 fatty acids, which can cause inflammation if you consume too much of them. Seed oils are present in processed foods, like tortillas.

Most of the soy we consume actually comes from soy oil, which accounts for 10 percent of the total calories produced by the American food industry.

So we’ve listed foods to avoid, but which foods then should you eat?

A healthy diet should contain a lot of meat, seafood and eggs, as well as foods that contain the “right” kinds of fat. Such choices are protein-rich, and protein helps the body grow, recover from an injury or a strenuous workout, and in general is one of the more satiating nutrients.

Eggs are packed with essential acids and vitamins. Even the cholesterol in eggs can be good for you, if you maintain a well-balanced diet.

Fat is also important because it gives you energy. It’s important to remember that the energy from fat is much better for your body than the energy you get when you eat carbohydrates.

So seek out monounsaturated fats, found in olives, and saturated fats, found in eggs and butter. Don’t be misled by the undeserved bad rep that saturated fat has had in recent years. The myth that all saturated fat clogs your arteries is based on outdated evidence that has since been disproved.

Avoid trans fats, or artificial fats found in processed foods, and “bad” saturated fat, found in refined carbohydrates, such as breakfast cereals. The saturated fat in refined carbohydrates can promote insulin resistance and inflammation – but this is not the case with saturated fats from meat.

And of course, fruits and vegetables are very important. Vegetables are packed with nutrients and healthy carbohydrates, and also offer anti-inflammatory properties.

If you don’t like vegetables, it’s probably because you haven’t had them prepared correctly, or you’ve simply become too accustomed to sugary or fatty processed foods. Bottom line: You’re an adult now. Eat your vegetables!

While fruits are high in vitamins, they’re not quite as nutritious as vegetables. Fruits also contain fructose, a sugar that can be harmful if you consume too much of it. Fructose metabolizes like alcohol, and can cause general inflammation or even liver damage.

However, most people who consume too much fructose actually do so through eating foods with high-fructose corn syrup – not by eating fresh fruit. So don’t skimp on the fruit in your diet!

Most people eat without thinking much about how they are putting food in their bodies, whether in front of the television or on the run. If this is you, it’s time for a change!

Eating right starts with listening to your body. Your body tells you what you need. If you listen, you don’t even need to count calories! Try the following tips.

First, eat your meals in a relaxed fashion, ideally while sitting at a table. Turn the television and your smartphone off, and chew slowly. When you gulp your food, your body’s hormones don’t have time to effectively process what’s landing in your gut. A meal should take at least 15 minutes to eat!

Be sure to eat three meals a day. Don’t snack! Space out your meals four to five hours apart; doing so helps keep your leptin levels in balance, allowing your body to adequately determine whether you’re full or not.

Don’t drink caffeinated beverages after midday, either. Caffeine can suppress your appetite and keeps you awake.

You may get cravings when you first try to adjust your diet, but do what you can to resist them. It’ll get easier over time!

Here are some rules to follow for each meal.

Base each meal around a protein source, with one to two palm-sized servings of protein. This means if your protein source is eggs, you can hold more than one egg in your hand – so eat two eggs!

The rest of your meal should be made up of vegetables. It’s okay to add spices and salt; you won’t consume too much salt anyway if you avoid processed foods altogether.

Eat fruits too, but they shouldn’t replace your vegetables. Each meal should also contain one or more sources of fat, such as olives or avocados. In a well-balanced, healthy diet, these kinds of fats won’t make you gain weight.

Don’t reduce the amount you eat, either! You won’t lose weight simply by eating less. Healthy weight loss takes time. You’ll lose weight as your body adjusts to your new eating routine.

Baby steps don’t work when you’re trying to make a big change in your lifestyle. You need a radical change to break bad habits, or you’ll just fall back on them.

That’s why the Whole30 plan is so effective. The Whole30 plan aims to reset your metabolism in just 30 days and stop your unhealthy food cravings.

The first phase is the process of elimination, during which you only eat healthy foods. Be strict. Don’t just try to recreate your favorite unhealthy foods with healthier ingredients, as this only makes you dwell on what you can’t really have.

You can allow yourself some processed foods, such as canned olives, but don’t eat anything containing monosodium glutamate, sulfites or additive carrageenan. Monosodium glutamate has deadly neurotoxins; sulfites can cause pulmonary problems; and additive carrageenan can cause inflammation.

This phase isn’t easy, and you might feel yourself going through withdrawal as you cut out excess salt and sugar from your diet. Stick with it! These tough cravings will soon pass.

After the first 30 days, the second phase of the Whole30 is reintroduction. It’s in this phase where you can start, slowly, eating some unhealthy foods again. During this phase you can explore legumes, non-gluten grains and dairy products, while at the end reintroducing grains with gluten.

After you reintroduce a certain food, go back to healthy food for a day and see how your body feels. And only reintroduce the foods you truly miss – remember, listening to what your body is telling you is crucial. If you reintroduce something that makes you feel bad, get rid of it and stick to your healthy choices.

Remember: this change is permanent. If you feel yourself slipping back into old habits, restart yourself on the Whole30. It’s a marathon, not a sprint! Even if you occasionally mess up, you’ll never go back to square one once you’ve started. You will learn how to best tune into your body and its needs!

The key message in this book:

The food you eat has a big effect on your mood, psychology, immune system and strength. So give your diet the attention it deserves! Avoid grains, dairy products and unhealthy fats, and make sure you get plenty of protein, vegetables and fruits. Kick start your metabolism and suppress your cravings with the Whole30 plan, but don’t lose hope if you slip up now and then. The Whole30 plan makes you healthier and stronger for life!

Actionable advice:

Avoid smoothies.

Fruit is important in a healthy diet, but don’t make your main fruit consumption come from smoothies. Liquid calories just don’t fill you up as much as solid calories can. So it’s best to eat fresh fruit in small servings throughout the day.

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Suggested further reading: The Fast Diet by Michael Mosley and Mimi Spencer

The Fast Diet (2013) is a guide to intermittent fasting and its health benefits. The 2015 edition includes a revised and expanded theory behind intermittent fasting, along with advice for physical exercise.