As a personal trainer in London, I’m asked this question by a lot of my clients. Some want to bulk up and build muscle, others want to lose weight and get slim. There’s a growing trend in high-protein low-carbohydrate diets (Zoe Harcombe’s diet, and the Dukan Diet are just two examples). But is high-protein good for you? Is it possible to eat too much protein?
What is protein?
Protein is one of the macro-nutrients essential to health, the others being carbohydrates, and fat. What makes protein unique is that it contains nitrogen in its chemical structure. The building blocks of protein are amino acids (‘amino’ means ‘nitrogen containing’). There are 20 different amino acids, each with different size, proportions and structures of 4 chemical elements: carbon, hydrogen, oxygen and nitrogen.
You might have heard the term ‘essential amino acids’. This means we need them from food, the body can’t make them, and there are 9 essential amino acids. The other 11 are called ‘non-essential’ , not because they’re not important, but because the body can synthesize them from the essential amino acids.
Foods containing protein can be categorized into ‘complete proteins’, and ‘incomplete proteins’. Complete proteins contain all the essential amino acids in sufficient proportions and quantity to make all the non-essential amino acids to meet our physiological needs. Incomplete proteins are foods that contain insufficient essential amino acids to make all the non-essentials.
All animal sources (such as meat, eggs, fish) are complete proteins. Most vegetable sources of protein (such as lentils, rice, kidney beans) are incomplete, but in the right combinations eaten together, they become complete (such as brown rice and beans eaten together). So it is possible for vegetarians to get all their protein needs from non-animal sources, but they need to eat the right combination and quantity of foods to achieve this.
When we digest protein, it’s broken down by stomach acid (denatured) and further broken down by digestive enzymes in the stomach and small intestine, into amino acids which can then be absorbed into the bloodstream.
Why do we need to eat protein?
The simple answer is for the amino acids, which enable repair and growth of our muscles. But amino acids have a much bigger role than just muscle repair and growth. They repair and grow all the cells of our body, including scar-tissue, hair, nails, even blood cells. All these cells, from muscle cells right through to fingernail cells, are made of protein.
Amino acids also build proteins called enzymes (needed for digestion), and hormones (molecules which send instructions for various biochemical reactions in the body), and chemical messengers of our nervous system.
Our immune system needs amino acids to build another kind of protein called antibodies, which attack foreign invaders such as viruses, bacteria, and toxins. So without enough protein in your diet, you’re more vulnerable to infections and illness.
Amino acids even help maintain your fluid and electrolyte balance. The right amount of fluid in the blood, and in the cells of your body, are crucial for your body to function correctly. And the right balance of electrolytes is essential for the function of your heart, lungs and brain.
Finally, protein can be synthesized for energy. The nitrogen component of amino acids is stripped off and made into urea in the liver, then sent to the kidneys to be excreted as urine. The remainder is converted into glucose for our energy needs, if we’re lacking in energy from carbohydrates and fats. Even when there’s plenty of energy from carbs and fats, protein contributes around 10% of our energy needs, even at rest.
How much protein should we eat?
The government’s recommended daily amount is around 15% of our total calories. In quantity, the general advice is to eat 0.36g of protein for every gram of body-weight. But the more accurate answer is that we might need more than these figures, depending on our height, weight, body fat percentage, gender, activity levels (and types of activity), and state of health.
‘How much protein should I eat’ is really three questions: how much protein as a proportion of total calories, and how much protein in total grams per day, and how much per meal?
The general advice issued by government for recommended daily amounts of protein is for a population of fairly sedentary individuals. If you’re more active, or aiming to build more muscle, you’ll need more protein. Up to 30% of your total calories as protein is probably safe (depending on all the variables such as activity levels), anything above that proportion risks a range of health problems.
There’s no way your body needs more than 30% of your total calories as protein (as long as your total calorie intake is at a healthy minimum level, around 2,000 calories a day for women, and 2,500 for men). Your body will simply burn the excess as fuel, and eliminate the nitrogen component in the urine, which overloads your liver and kidneys. Burning large amounts of protein as fuel puts your body into a toxic state, known as a ketonic state, which is one of the risks of high-protein low-carb diets.
Remember, the body’s preferred energy source is carbohydrates, which is why it’s healthy to eat around 30 -40% of your total calories as carbs (natural complex carbs, not processed junk!).
A common piece of advice is not to eat more than 30g protein per meal. This is too vague and general to be of use, because everyone is different in the amount of protein they need. It may well be that 30g per meal is right for you, but each person’s individual protein requirements depends on a whole range of factors (age, height, weight, activity levels, muscle repair needs, number of meals a day, and so on).
If I eat more protein, will I build more muscle?
The key trigger to building muscle is resistance exercise which breaks down muscle fibres, which then demand amino acids to repair and build the muscle. Simply eating more protein without exercising correctly won’t make your muscles grow bigger. Muscles will only grow to the extent that you overload them with exercise, sending a signal to repair and build in anticipation of future demands on the muscle.
So heavy workouts with progressive overload are necessary for muscle growth, but not sufficient. You need the building blocks of muscle growth, amino acids. So to build muscle, you need the right balance of exercise and protein consumption.
A simple guide to the maximum protein you should consume if you’re a male working out regularly and intensively in the gym with the aim of building muscle, is to eat 1 gram of protein for every pound of your body-weight. So if you’re 185 lbs, eat 185 grams of protein a day. This is more than double the recommended protein intake of a sedentary individual.
But make sure the proportion of protein you consume stays within the range of 20-30% of your total calories, or you’ll risk getting too little carbohydrates (a vital energy source) and possibly too little fat. A good ratio of carb:protein:fat would be 40:30:30.
And make sure you spread your protein consumption throughout the day, so your body has a steady supply of amino acids to meet demands throughout the day. If you eat too much protein in one meal (particularly if you’ve not just exercised), you’ll not only overload your digestive system (which has to work hard to break down protein into amino acids), but the excess will be burnt as energy, with the undesirable side-effect of toxic ketones. It’s a good idea to include some protein with every meal/snack.
Protein synthesis by the muscles is at its optimum level just after a heavy workout, so ensure your biggest protein consumption is within 1 hour after your gym session. For fast absorption of amino acids, choose a whey protein shake, to get the amino acids to your muscles as efficiently as possible post-workout.