For a FULL but very simple explanation of macros, please see this post.

CARBOHYDRATES

There are 3 types of carbs: simple/refined carbs, complex starchy carbs, and complex fibrous carbs.

“Simple” carbs have a simple molecular structure and get turned into energy (i.e. glucose) for your body very quickly and easily. They are you body's first line of energy, and include sucrose (regular table sugar), fructose (sugars found in fruits), and lactose (sugars found in milk).

"Complex starchy carbs" have a more complex molecular structure, and are often what people think of when they refer to “carbs” in general (e.g. rice, wheat, potatoes, etc.). Because it takes your body longer to break these down into glucose, you don't have the same blood-sugar spikes as you do with "simple" carbs. Beware, however, as often times what you end up eating are refined versions of these foods (e.g. white rice, white flour), which behave as "simple carbs".

"Complex fibrous carbs" are the “best” types of carbs. Since your body is unable to absorb fiber, these foods pass through the digestive system and play a crucial role in keeping your digestive system healthy. The most common source of complex fibrous carbs are vegetables. Yes, you heard that right… vegetables are carbs!

PROTEINS

Proteins are complex molecules made up of strings of amino acids, which play a vital role in your body’s structural and metabolic processes. There are 20 amino acids, of which 9 are considered “essential,” meaning the body is unable to produce them naturally... so we rely on food to fill this void.

From a nutrition perspective, protein helps you sustain your energy throughout the day, but it also plays a large role in building and repairing muscle and tissue, hormone regulation, enzyme manufacturing, and immune health.

FATS

First off, fats don’t make you fat. In fact, eating less fat than recommended can lead to consuming MORE sugar/simple carbs than recommended, thus starting a negative cascading effect that can undermine your wellness and nutrition goals. Fat plays a large role in keeping you satiated and helps improve brain function, while also playing a key role in vitamin absorption.

However, just as there are “good” and “bad” carbs, there are also “good” and “bad” fats!

"Unsaturated fats" are the good ones! Typically found in foods like avocados, fish, nuts, olive oil, and seeds, unsaturated fats can, among other things, improve cholesterol levels and aid in inflammation.

"Saturated fats" are typically found in animal foods (e.g. cheese, meat, milk) or in “tropical” oils (e.g. coconut/palm oil). There’s debate around the health implications of saturated fats; however, as a rule of thumb, you’ll likely want to limit intake of them, and replace with healthy unsaturated fats instead.

"Trans fats" are bad! Most typically found in fried foods, baked goods, and processed snack foods, trans fats have been shown to raise the bad type of cholesterol (LDL) and lower the good type (HDL). They’ve also been linked to heart disease, stroke, and diabetes, and can contribute to insulin resistance.

Your body breaks down food (namely carbs) into glucose, which it then uses for quick energy. However, your body only needs so much glucose at once.

Any excess glucose gets stored as glycogen in your muscles and liver for later use (typically to maintain blood glucose levels during exercise).

If these glycogen stores don't get depleted, over time they turn into fat cells!

In short, your body first uses glucose for energy, then it turns to glycogen stores, then finally fat stores.

It's a cascading pattern where excessive "simple carb" intake (which very easily becomes glucose) prevents glycogen stores from being sufficiently depleted, thus never allowing the body to use fat stores for energy.

Hopefully you can now see why consuming excessive simple carbs is so detrimental to shrinking that waistline!