Protein Power: Why Your Body Can't Thrive Without It - Part 1

Part 1 of the Protein Power Series  |  By Sarah Flower, Registered Nutritionist

Protein. It's one of those words that appears on every food label, in every fitness article, and in virtually every health conversation going. But the noise around it has created as much confusion as clarity. In this five-part series, I want to cut through that and give you a proper, grounded understanding of what protein actually does, why so many of us are falling short, and what you can do about it.

Let's start at the very beginning.

What Is Protein and Why Is It 'Essential'?

Protein is one of three macronutrients, alongside fat and carbohydrates. But unlike those two, protein is classified as essential. That's not just a marketing word; it has a specific biological meaning. It means your body cannot produce sufficient protein on its own and must obtain it consistently through food. Carbohydrates are not classified as essential in this way because the body can produce glucose from fat and protein if needed. Protein and fat are the true non-negotiables.

Proteins are made up of amino acids. There are 20 of them in total, and your body uses them in over 50,000 different ways. Nine of these are classified as essential amino acids, meaning they must come from your diet because the body cannot synthesise them at all. The other eleven can be made internally, though often not in sufficient quantities when you're under stress, recovering from illness, or not eating well.

Far More Than a Muscle Story

When most people hear 'protein', they think muscle. And yes, muscle building and maintenance absolutely depend on adequate protein. But that's a fraction of the picture. In my clinic, I often describe protein as the body's architect and maintenance crew, working around the clock on a list of jobs most people never think about.

What Protein Does Every Single Day

Hormones. Insulin, glucagon, thyroid hormones, leptin, all proteins. When protein intake is too low over time, hormonal imbalance can follow, showing up as fatigue, weight changes, poor sleep and disrupted mood.

Enzymes. Every metabolic reaction your body runs, digestion, detoxification, energy production, depends on enzymes, which are proteins. Without sufficient protein, these processes can't function properly.

Immune defences. Antibodies are proteins. If you're someone who catches every bug or struggles to recover from illness, it's worth looking at your protein intake.

Neurotransmitters. Serotonin, dopamine, GABA, the mood and brain chemicals that influence how you feel, sleep and concentrate, are all synthesised from amino acids. Low protein is a commonly overlooked contributor to low mood, brain fog and disrupted sleep.

Skin, hair and nails. Collagen, elastin and keratin are proteins. If these are struggling, dietary intake is always worth examining before spending money on topical products.

Tissue repair. Whether your body is healing a wound, rebuilding gut lining, or recovering from exercise, it draws on your protein reserves. When those are depleted, recovery slows across the board.

Fluid and pH balance. Proteins like albumin help maintain fluid balance between cells and blood vessels, and others act as buffers to keep blood pH stable.

Transport. Haemoglobin carries oxygen. Ferritin stores iron. Both are proteins. The body's internal logistics system runs on them.

Complete vs Incomplete Protein

Not all protein sources deliver the same thing, and this becomes particularly important for anyone eating a predominantly plant-based diet.

Complete proteins contain all nine essential amino acids in adequate proportions. These are found in animal foods, meat, poultry, fish, eggs, dairy, and in a small number of plant foods: quinoa, soy, hemp seeds, and buckwheat.

Most plant proteins are incomplete, meaning they're missing or low in one or more essential amino acids. Beans, lentils, most grains, nuts and seeds fall into this category. This doesn't make them unhealthy, but it does mean you need both variety and quantity to get the full amino acid profile, something that requires conscious planning.

Protein and Metabolism

Protein has something the other macronutrients don't: a significant thermogenic effect. Your body burns around 20–30% of the calories in protein just through the act of digesting it, compared with roughly 5–10% for carbohydrates and 0–3% for fat. This means a protein-rich diet actively contributes to a higher metabolic rate simply by existing on your plate.

Beyond metabolism, protein is particularly effective at reducing hunger. It suppresses ghrelin (the hunger hormone) more effectively than carbohydrates or fat, and it increases satiety hormones like peptide YY. The result is that you feel fuller for longer, with fewer cravings and better appetite control throughout the day.

Protein, Muscle and Ageing

From around our mid-thirties, we start to lose muscle mass naturally, a process called sarcopenia that accelerates after 50. This isn't just a cosmetic concern. Muscle is metabolically active tissue: the more of it you have, the more calories you burn at rest, and the more efficiently your body manages blood sugar, hormones and energy.

During weight loss, including for those using GLP-1 medications, there's a real risk of losing muscle alongside fat, sometimes as much as 15–20% of total weight loss if protein isn't prioritised. Adequate protein, alongside some resistance activity, is the primary way to protect against this.

Are You Getting Enough?

Here's where it gets uncomfortable. Most people are not eating as much protein as they think. A small chicken breast in a curry with rice, once you account for the sauce and the portion size, might deliver as little as 15g. That's not a lot.

Current UK guidelines suggest 0.75g per kilogram of body weight per day. In clinical practice, this is widely considered too low for most adults, and significantly too low for anyone over 40, under stress, trying to lose weight, or going through perimenopause or menopause. A more realistic starting target is 1.2–1.6g per kg of body weight, and sometimes more.

A Quick Snapshot of Real Protein Numbers (per 100g)

Food	Protein (g)	Net Carbs (g)
Chicken breast (cooked)	27–30g	0g
Eggs (approx. 2 large)	13g	1g
Salmon (baked)	25g	0g
Greek yoghurt (full fat)	9–10g	4g
Firm tofu	12g	1.9g
Lentils (cooked)	9g	12g
Quinoa (cooked)	4g	21g

Practical Ways to Increase Your Intake

•       Eat protein at every meal and snack, including breakfast. Most people front-load carbohydrates at the start of the day and wonder why they're flagging by mid-morning.

•       Spread intake across the day rather than saving it all for dinner. Distributing protein more evenly supports better muscle protein synthesis.

•       Build meals around the protein source, not the carbohydrate.

•       Batch cook protein-rich basics, chicken, hard-boiled eggs, legumes, so they're ready to go.

•       Swap carb-heavy snacks for boiled eggs, Greek yoghurt, cheese, or nuts.

What's Coming in Part 2?

In Part 2, I'll be pulling apart the 'high protein' label, what it actually means under food law, why it can be genuinely misleading, and how to read a product properly to understand what you're really getting. Spoiler: the front of the packet tells you very little.

Until then, take a look at your meals today. Where is your protein coming from, and is there more you could do to make it work harder for you?

Sarah Flower is a registered clinical nutritionist with over 30 years of experience, specialising in gut health, hormones and metabolic health. She works with clients across the UK from her clinic in Exeter and via Zoom.

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