Nonsensical nutritional claims have been with us for years. Stanley Green, the Protein Man, paraded up and down Oxford Street warning against the dangers of protein for 25 years until his death in 1993, his placards proclaiming gems of protein wisdom such as ‘Less lust, by [sic] less protein.’
Today’s nutribabble comes in the form of high-protein diets. Food manufacturers are offering high-protein versions of everything from Weetabix to Mars bars, along with supplements, powders and snack bars.
Protein makes up the structures of hair, nails, muscle and other tissues, enzymes, hormones and molecules that transport nutrients in the body. When we eat food, the protein is broken down into amino acids in the stomach and then absorbed in the small intestine. The liver sorts out which amino acids the body needs and breaks down those it does not need into urea and ammonia. Excess protein is not stored but excreted by the kidney in urine mainly as urea.
Humans have slow rates of growth and relatively low protein requirements compared to other animals such as pigs. As a rule of thumb roughly 10 per cent of food energy needs to be supplied by protein. On average, protein provides 15 per cent of the energy in the British diet, with 35 per cent of the intake coming from meat, 22 per cent from cereals and 14 per cent from dairy products.
Animal proteins generally provide all the essential amino acids required but the proteins in cereals are deficient in lysine. This is of no consequence if they are consumed with legumes, which are high in lysine. For example, baked beans on toast will meet requirements for the essential amino acids. This explains why even vegans have adequate intakes of protein.
Protein has a growth promoting effect when demands for growth are high. However, once growth has ceased, extra protein does not promote growth. Whey protein is a by-product of cheese-making and has long been known to promote growth in pigs. Hence the association of Melton Mowbray pork pies with stilton production or Parma ham with Parmesan where whey was put in pig swill.
Whey protein is cheap, about $0.9 a pound, but commands a 10-fold greater price when sold as a protein supplement to body builders. The whey protein supplement industry (worth $9.2 billion in 2015) seems to have been telling porky pies. An application for official endorsement of the health claims that whey protein increased muscle mass, muscle strength, endurance capacity, muscle fatigue and repair was trounced by the European Food Safety Authority in 2010. A recent high-quality trial found no effect taking whey protein on top of a normal diet on muscle protein synthesis in older men.
There are many reasons why high-protein diets (more than 20 per cent of energy) are not healthy. They increase the rate of loss of calcium from bones, have adverse effects on pregnancy outcome, are toxic to people with renal or liver disease and are probably best avoided in people with diabetes. Large, long-term observational studies consistently find that people who eat a lot of meat, particularly red meat, sausages and burgers, are more likely to be overweight, develop type-2 diabetes, and die from cardiovascular disease and colon cancer.
The Paleo diet paints a rosy picture of Paleolithic man and advocates a high-protein diet consisting of mainly meat and fish, eggs, nuts, with some fruit and vegetables, but recommends avoiding any processed food including cereals, legumes and dairy products.
However, this diet is based on speculation, as there are no written records. Our knowledge of indigenous hunter-gatherer nomads suggests that their lives were harsh and short. For example, the life expectancy of the Arctic Inuit was only about 28 years. Cereal cultivation and the development of food processing provided food security and allowed the establishment of human settlements, the domestication of animals and caused civilisations to flourish. Indeed, wheat was the key food commodity underpinning Roman civilisation. The labelling of gluten-free products for the benefit of the one per cent of the population with coeliac disease has wrongly encouraged people to think they need to avoid wheat and other cereals.
Increasing protein intake does not increase loss of body fat. While lean meat and fish are quite satiating foods, this is not the case for bacon, sausages, burgers, cheese and salted nuts. Maintaining an adequate intake of protein on a reduced energy intake is important to prevent loss of lean tissue. This is easily achieved by eating everyday foods. For example, porridge with milk for breakfast, a bowl of pea soup with bread, a chicken breast and a small piece of cheese provide enough protein.
Nobody took the Protein Man seriously with his proclamation that protein increased lust. What worries me is that social media and the web have allowed nutribabble to flourish, spreading wrong-headed information, offering false hope and peddling dangerous dietary advice.
Tom Sanders is professor emeritus of nutrition and dietetics at King’s College London