Those who are on LCHF or Ketogenic type diets often ask how much protein they should eat and if consumed in excess, will this have a detrimental effect on their kidneys?
What are the Claims
Claims are often bandied about that a high-protein diet can cause damage to the kidneys and increase the risk of cancer because if takes longer to digest and eliminate from the body. However these claims simply aren’t supported by sound scientific research. The research does show that people with pre-existing kidney damage or dysfunction should restrict protein intake, but a high-protein diet has never been shown to cause kidney damage. In fact a high-protein diet has been shown to improve blood glucose and lowers blood pressure, and will improve health, body composition and performance in the physically active.
The widely held myth that meat, as a protein source, stays in the gut longer than other foodstuffs probably stems from the fact a high-protein diet results in a lot of leftover ammonia, which must be removed in the form of urea by the kidneys. This uses extra water and if you don’t drink more to compensate, the dehydrating effect can result in constipation. It’s important to realise that meat, vegetables (and chewing gum!) all move – and exit – together.
How much Protein do we Need?
About 20% of your body is made up of protein, the main building blocks of the body. Proteins are used by the body to make muscles, tendons, organs and skin, with the amount of protein required each day being dependent on the individual and their specific needs. For example if you are a body builder, you will be trying to pack in as much protein as you can to repair and build muscle but there is no magic number of grams per day that suits everyone.
Because your body does not store protein, you need to get enough from what you eat each day. Protein can be categorized into two types: complete and incomplete and are formed from amino acids. The amount and type of each amino acid varies based on the protein source. Our body requires twenty-one distinct amino acids to produce proteins. 12 of these are created by the body itself while the other 9, called “essential” amino acids, have to be obtained from our diet. Both plants and animals are a source of protein, and depending on which end of the continuum you subscribe to concerning “meat v plant” diet regimes, you will get contrasting views of which type of protein is superior. Complete proteins contain all of the amino acids your body needs and include meat, fish, poultry, dairy, and soy products. Foods that are lacking or are very low in one or more essential amino acids, the “incomplete proteins” include beans, grains, nuts, and vegetables. Protein is not just about quantity but also about quality.
Some suggest that the body can only absorb about 30g of protein per meal and anything over this would simply be excreted. This is not strictly true, as even though there is a limit to how fast your body absorbs protein, and our body does not store protein long term, it does “reserve” proteins for a time. Excess protein will reside in your gut for a time until its turn to be absorbed. The 30g limit was a tenet of the body builders approach to nutrition assuming 10g per hour absorption with a meal every three hours. Research done on Intermittent Fasting however supports the theory that your body can cope with far more protein than most people think. Studies showed that there was no difference in effective protein absorption between several small meals verses one large one containing an average of 80-100g of digestible protein.
While it is excepted that sedentary people don’t need as much protein as those that exercise regularly, research shows that anything less 1 gram per kg of bodyweight is not enough to maintain lean mass and bone health as you age. Therefore a person weighing 70kgs needs to eat at least 70g of protein in a day.
How Protein is Processed in the Body
Dietary proteins (the amino acids) that are residing in the gut will be absorbed into the intestines, and later into the body. The muscles of the intestines move food forwards and backwards in order to extract all the nutrients and the rate of travel depends on how much indigestible fibre and water there is. Study’ show that the amount of protein absorption by the small intestine tends to be around 95% when 10-50g of protein is consumed, with an hourly uptake of around 5-10g per hour, with animal sources a bit higher than plant. Certain hormones also enable the body to self-regulate digestion or slow down intestinal contractions and speed in order for all the present protein to be absorbed.
According to the “Mayo Clinic” it normally takes up to 24-48 hours to digest red meat with a quantity of the proteins being absorbed by the gut to maintain “gut health” while the remainder of the amino acids float around in the blood system to fuel muscle growth and repair body systems. Even with the small intestine retaining a pool of amino acids waiting to be released, when needed, eventually the unabsorbed fragments carry on to the colon to be fermented by bacteria.
A final note. One way of checking if you are eating more protein than is being absorbed, is to take the sniff test! If after a bowel movement there is a very bad smell, you can be assured that protein is being lost in the faeces and not being taken up by the gut or muscle.