What’s the deal with protein?

Protein. Take a moment to pause and notice the associations that word has for you. Are you a gym rat, then this might be essential to get those gains. Are you plant-based, then you might get a lot of questions about whether you’re getting enough. Or maybe you know that somehow it is quite important, but not exactly why.

Some amino acids can be produced by the body, some cannot - these essential amino acids need to come from our diet, or we’ll be in pretty bad shape. In order to make sure we stay healthy, our brain regulates the lowest amount of protein we can eat - around 5 to 14 percent of daily food and drink intake. If our protein intake makes up less than that, our brain switches on neural pathways that make us ravenously hungry, so that we increase our food intake - even if we have met our energy needs for the day. This is called protein leverage [1] and it’s a protective mechanism: if we don’t eat enough protein for a while, our body will get its amino acids from breaking down our skeletal muscle, and after some more time, protein malnutrition sets in, which brings a whole host of nasty symptoms.

On the other side of things, there is no clear upper bound of how much protein we can eat, it depends on a lot of other factors. It’s been documented however that eating too much protein results in strain to our liver, kidneys and vascular systems. Experts today seem to agree that there is a sweet spot for protein consumption, to keep us healthy, and that seems to be from around 0.8g of protein per kg of bodyweight, up to 2g of protein per kg of bodyweight (see additional remarks below) [2-5].

The 20th century saw a boom in high-protein diets, with the food industry catering to people’s desire to lose weight while keeping their muscle mass. This started with the Atkins diet, which leverages protein’s influence on satiety to help with eating less and losing weight6. In general, this translated to the practical advice of having a high animal-protein diet. However, there are potential risks to eating too much protein, as we already discussed, including not eating enough of other types of nutrients. For example, fibre cannot be found in animal sources of protein, but is abundant in many of the limited foods on the Atkins diet: grains and starchy vegetables. A renaissance of the high-protein craze came in the 21st century with the explosion of “ancestral” type diets, from paleo to carnivore, which are advertised as being high in animal protein (in some cases, almost only consisting of meat) [10]. The pseudo-scientific argument goes that “eating meat made us human” and a high-meat diet is what we are “evolutionarily primed” to thrive on. Several studies have debunked this claim, but it still remains a popular excuse to indulge in a high-meat diet (see additional remarks below) [10–12].

Generally speaking, obtaining adequate amounts and quality of proteins (i.e., all essential amino acids in a well-balanced diet) is not a problem in developed countries. As Sandra Mikhail puts it, “if you’re eating enough calories, you’re eating enough protein. We only see cases of too low protein intake in some clinical cases of eating disorders, where total calorie intake is inadequate.”

First, eating meat is quite expensive for our health. Some popular protein sources, like red meat and processed meats, have been classed as Class 2A and Class 1 carcinogens respectively [13]. The jury is still out about other forms of animal protein [14], but some studies have shown that they may harm human health as well [15,16]. Beyond the known carcinogenic effect of red and processed meat, we also know that high meat consumption is linked to poor vascular outcomes. Studies have shown that high-meat diets may lead to more atherosclerosis, heart attack and stroke. Moreover, high meat diets tend to be low in fibre, a crucial macro-nutrient that keeps your system regular and our gut microbiota happy, which is being increasingly seen as a human “organ” in its own right [17].* Fibre is a type of carbohydrate, but it is indigestible for the human host. However, the trillions of gut microbes living in our gastro-intestinal tract need to eat too, and fibre is their main source of nutrition. In exchange for feeding them, the gut microbiota produces a wide variety of chemical compounds (with probably many of them as yet undiscovered) that are beneficial for our health [18]. It has been observed that those eating meat have less diverse and different microbes in their gut than people eating a plant-centric diet [21,22]. While we don’t exactly know what a healthy gut microbiome looks like, we do know that the more diverse the species of microbes we host, the better.

Secondly, production of animal protein is expensive for our planet. Animal farming specifically is a major contributor to global warming and loss of biodiversity. Livestock farming and fish farming together make up 15% of global greenhouse-gas emissions [19,20], yet only account for ⅓ of the global protein supply [23]. It’s also a very inefficient use of our crops, as it takes 9 kcal of crops to create 1 kcal of meat [24]. As Laura Sommer, an expert in food systems, puts it “it takes a lot longer for meat to get into your stomach, so it needs more resources along the way”, while plants “can grow and we can eat them directly from the field”. Further, large areas of land are being cleared in the amazon rainforest and other carbon sinks to plant crops for animal feed [25–27]. Tofu, a very popular plant-based protein used in all sorts of dishes, on the other hand, doesn’t have this problem [28]. When thinking about sustainable sources of protein, Sommer points to two key factors to consider: 1) how it was produced (plants vs. animals, factory farming vs. small local farm), and 2) how much you eat (maximum 300g per week of meat according to the EAT-Lancet commission [29]).