Almost every client I’ve ever worked with came to me confused about calories. Not because they’re stupid — because the information out there is a mess. One camp says “a calorie is a calorie, just eat less.” Another says calories don’t matter at all and it’s all about cutting carbs, or sugar, or eating in some magic window.

So I wrote a book about it. The Guide To Calories is a fully designed, properly referenced guide — awareness, intake and output — and it’s the first volume in my PG Fitness book series. I’m giving it away completely free, no catch and no email hostage-taking. This post walks you through what’s inside, and you can grab the full book at any point with one click.

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The Guide To Calories

14 designed pages · awareness, intake & output · backed by 12+ peer-reviewed references. Yours free, straight to your device.

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Why I Wrote This Book

The intention of the guide is simple: to give you the tools to become genuinely aware of calories — your intake, your output — and how to manipulate both the quality and the quantity of them to fit your own goals.

Here’s the honest starting point I use in the book: if you’ve picked it up at all, your current habits and behaviours around food don’t align with the physical outcome you want. That’s not a judgement — it’s the most useful diagnosis in fitness. Whether your goal is changing your body composition, improving physical and cognitive performance, or both, the energy you consume every day is the fuel for all of it. Understand the fuel, and you’ve taken the biggest single step in the right direction.

What Exactly Is A Calorie?

A calorie (or kilocalorie — kcal) simply indicates the amount of energy in an item of food or drink. Once digested, that energy does two jobs: first it keeps you alive — breathing, digestion, circulation, cell regeneration — and second it fuels everything you choose to do on top, from walking the dog to a heavy leg session. Depending on where the calorie comes from, it may also deliver the nutrients your body can’t do without: dietary fibre, amino acids, antioxidants, vitamins and minerals.

All of your calories arrive from just four places, each carrying a fixed amount of energy per gram:

That last one matters more than people like to admit: alcohol is made by fermenting and distilling natural sugar or starch, and at 7 kcal per gram it’s nearly as energy-dense as pure fat.

Are All Calories Created Equal?

When it comes to the laws of thermodynamics — yes. A unit of energy is a unit of energy, and when we’re controlling someone’s intake for body-composition purposes, the numbers count. Calories in versus calories out is still the major determining factor in whether your body changes. On paper, you can lose body fat eating anything you want, provided the energy going in is less than the energy being used.

But “on paper” is doing a lot of heavy lifting in that sentence — and this is where the book separates itself from the shouting matches online. Two foods with identical calories can behave very differently after you eat them. The first reason is the thermic effect of food (TEF): your body spends energy digesting, absorbing and storing what you eat. And the spend varies enormously by macronutrient:

• Protein: digesting it costs around 20–35% of the energy it contains — eat 100 kcal of protein and you use 20–35 kcal just processing it.
• Carbohydrates: roughly 5–15% of the energy consumed.
• Fats: at most 5–15% — the cheapest macronutrient for your body to store.

The second reason is nutrients. Foods stripped of fibre, amino acids, antioxidants, vitamins and minerals — what the book calls empty calories — make managing energy balance much harder. Manufacturers add solid fats and sugars to processed food (and alcohol) precisely to make it more enjoyable and easier to over-consume. Ask anyone which foods they routinely overeat and the answer is almost never plain chicken and spinach — it’s the engineered stuff combining solid fats with added sugars like sucrose or high-fructose corn syrup.

Energy Density vs Nutrient Density

This pair of ideas is the engine room of the whole book, and once you’ve got it, food shopping never looks the same again.

Energy density is the number of calories in a given weight of food. Energy-dense foods pack a lot of calories into a small serving — typically high in sugar and fat, low in water. Nutrient density is the amount of fibre, complex carbohydrate, amino acids, antioxidants, vitamins and minerals in that same weight of food.

The book’s example: ice cream versus spinach. Ice cream crams a pile of calories from sugar and fat into a tiny serving, with bundles of taste and almost no nutrients. A whole plate of spinach barely registers any calories, yet it’s loaded with nutrients. Neither food is “good” or “bad” — they’re just at opposite ends of two scales, and the proportion of your diet each end occupies is what decides how hard or easy your goals are to reach.

Taste & Satiety: The Two Things Nobody Plans For

Most diets fail for one of two reasons: the food doesn’t taste good enough to keep eating, or it doesn’t fill you up enough to stop eating. The book treats both as first-class problems.

Taste

Flavour isn’t trivial — it’s one of the most important human senses, built from odour, taste, temperature and appearance together. Food has to be perceived as appealing, not just satiating; research shows taste quality is critical to any long-term dietary compliance, and that a food’s taste, smell, texture, temperature, colour and appearance all affect how satisfying it is. If your “healthy” food is bland, your diet has a shelf life.

Satiety

Satiety is the feeling of fullness and appetite suppression after eating. Foods with high satiety protect you from over-consumption automatically — no discipline required. They share four characteristics:

• High in protein — research shows protein is the most satiating macronutrient of all, and it positively affects several satiety hormones.
• High in fibre — fibre adds bulk and slows digestion and stomach emptying, keeping you fuller for longer.
• High in volume — foods containing a lot of water or air fill the stomach for very few calories.
• Low in energy density — soups, stews, fruit and vegetables: heavy on the plate, light on the calorie budget.

Where Your Calories Actually Go

Managing intake is only half the equation. The book also breaks down your output — total daily energy expenditure (TDEE) — and the proportions surprise almost everyone.

The headline finding — and the one I push hardest with clients — is that NEAT accounts for far more energy than your workouts. Non-exercise activity thermogenesis is every step, stand-up, stair climb and fidget of your day. An hour in the gym cannot compete with the other fifteen waking hours; habitual daily movement is the most under-rated fat-loss tool there is. Train hard, absolutely — but move more, everywhere, always.

How To Read A Food Label

The book includes a full plain-English tour of UK food labels — energy (kcal and kJ), carbohydrates and the “of which sugars” line, fat and “of which saturates”, protein, salt, and serving sizes. A few of the rules that change how people shop:

• Always compare per 100g, not per portion — the manufacturer’s “portion” is rarely the serving you’ll actually have.
• Carbohydrates = fibre + starch + sugar. Look for foods with more starch and fibre; “of which sugars” tells you how much of the carb content is the simple stuff.
• Aim for 30g of fibre a day — nutrient-dense, filling foods are typically loaded with it.
• Ingredients are listed by weight, biggest first — the first three ingredients tell you what the product really is.

The Traffic Light System, Decoded

The front-of-pack traffic lights let you judge a product at a glance — red (high), amber (medium), green (low) for fat, saturates, sugars and salt. Selecting mostly green and amber typically means nutrient density and satiety both go up per calorie consumed. The actual thresholds, straight from the book:

One warning from the book: watch the serving size these are quoted against — it can be misleading on some products.

What’s Inside The Full Book

This post is the tour — the book is the toolkit. Inside the free PDF you’ll find every section above in full, properly designed and referenced:

• What calories are and the energy in all four sources — protein, carbs, fat and alcohol
• Are all calories created equally? Thermodynamics, TEF and empty calories
• Energy density vs nutrient density — with the foods to build around
• Taste, satiety and the four characteristics of genuinely filling food
• The complete breakdown of daily energy expenditure: BMR, NEAT, EAT and TEF
• A full UK food-label walkthrough — including fibre, starch, healthy fats and polyols
• The traffic light system with every threshold
• 12+ peer-reviewed references, so you know none of it is bro-science

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This Is Volume 01 — The Series

The Guide To Calories is the first book I’m featuring from the PG Fitness library, but it has company. Over the years I’ve written a whole shelf of guides for my clients — the Keto Book, the Eating Out Guide, Cooking Skills, the Guide to Hand Portioning, the MyFitnessPal Guide and the Menopause Guide among them — and I’ll be giving each one the same deep-dive treatment on this blog in the coming weeks.

Impatient? Good. The entire range is already free on the downloads page — help yourself.

Key Takeaways

• Calories are units of energy from four sources: protein (4 kcal/g), carbs (4), fat (9) and alcohol (7).
• Energy balance — calories in vs calories out — decides whether your body composition changes. That part really is just physics.
• But food choice decides whether you can sustain it: protein’s thermic effect (20–35%) and the satiety of high-fibre, high-volume, nutrient-dense food make the same calorie target feel completely different.
• BMR burns 60%+ of your daily energy, and everyday movement (NEAT) out-burns the gym (EAT) — move more, everywhere, always.
• Read labels per 100g, hunt the hidden names for added sugar and fat, target 30g of fibre a day, and favour green and amber traffic lights.
• You don’t build habits by stopping things — you build them by starting things. Start with the free book below.

Disclaimer: This article and the book it describes are for general education and are not medical or dietetic advice. Calorie needs are individual — if you have a medical condition, a history of disordered eating, or are pregnant, speak to a qualified professional before changing your diet.