Spot-quiz. Which of these foods can you eat every day as your protein injection and still be healthy, as recommended by the American Heart Association? A McDonalds quarter-pounder? A 4-oz chicken breast (no skin, grilled)? 4oz Cheddar cheese? 4oz unsalted organic almonds? Two large eggs?
The answer, of course, is none of them. Because the recommended daily intake of protein is actually 0.8 grams per kilo of bodyweight. Which means that a 140lb woman should be eating 112g - or slightly less than 4oz - of protein a day, all up. Not at every meal: altogether. Worryingly, that's the sort of serving most people will eat as a snack, with a side order of fries, before going home and demanding to know what's for dinner. If it's any consolation, your average vegetarian is probably gorging on considerably more than their recommended daily allowance in the form of nuts and eggs and tasty cheese.
In the West, all but the diets of the very poor have always been heavy on protein, despite the rather addled picture that's been painted over the top of history. A quick scan of a dictionary will inform you that "meat", until really very recently, actually meant red meat - beef, mutton, venison and so forth. So all those references to; "we only ate meat once a week, on Sundays", are completely honest: it just doesn't take into account all the chicken, sausages, offal, rissoles, rabbit, bacon and pork chops we ate the rest of the week.
Amazingly, there are signs that even this surprisingly small allowance might be revised downward in years to come. Because according to a study by Washington University in St Louis, there may well be a link between the consumption of protein and higher levels of cancer.
This doesn't actually come as a huge surprise, as certainly there's been a suspected link between high-meat diets and some forms of bowel cancer for years, but this one's a bit more detailed and considerably more controlled. Three groups of people (though there were only 21 of each, mind) were studied: those with a sedentary lifestyle and a normal western diet (with its high levels of sugars, processed refined grains and 1.23g of protein a day); endurance runners on a normal (but high-protein - 1.6g, as is customary among athletes) western diet; and people on a low-protein (0.73g), low-calorie diet. Each was measured for levels of the growth hormone IGF-1 (which promotes cells proliferation) which has been linked to pre-menopausal breast cancer, prostate cancer and certain types of colon cancer. And guess what? The low-protein people had a significantly lower level of the hormone in their bloodstreams.
This isn't, of course, a definitive study by any means. And it's just as interesting in terms of the fact that these people were also on a calorie-restricted diet - just under 2,000 a day - as that their diet had an unusual makeup to it. Funnily enough, they also weighed less than the other two groups. There is, of course, a well-established link between obesity and many forms of cancer. Furthermore, these bare stats don't actually reflect the source of all the subjects' protein intake. Modern factory farming involves pumping meat animals with large quantities of growth hormones, and it's a fair bet that this is going to have some effect at the consumer end.
The problem, of course, with these studies is how they relate to the First Rule of Nutrition. The First Rule of Nutrition is this: for every piece of scientific research which advances our knowledge of the relationship between the human body and the food it consumes, there will be a diet guru waiting to launch a fad eating plan based upon it which excludes all reference to any other knowledge, contradictory or complementary.
Put it another way. I just did a book-search on the word "diet" on Amazon.com and it came up with 183,537 results. 183,537: that's pretty much one title for every 2.4 McDonalds employees worldwide. And you can bet that every single one of them won't just be offering to make you lose weight: they'll be promising to make you healthier, too. Stand by for hit no 183,538: The Anti-Atkins: The Total Carbohydrate Route to Avoiding Cancer. Actually, I think I might write it myself. It must be worth at least two McSales.