Don’t believe the hype that high-protein diets can cause kidney disease and cancer, this is nothing but an urban myth that is not back by scientific evidence. Research has shown that high protein diets of up to 35% of calories (or even higher) are safe for people without pre-existing kidney problems and can help prevent cancer growth [1,2,3,4], getting enough glycine in the diet is essential. There is very little evidence that eating a high protein diet increase cancer risk, as long as you eat a well balanced nutrient-dense diet and removed processed meats from the diet. If you would like some more information read this article from Chris Kresser.
It's important to note that lean muscle meat and eggs are high in an amino acid called methionine, whereas foods like bone broth and fattier cuts of meat like shanks, ribs, chops, brisket and oxtail as high in and Amin acid called glycine. Consuming higher levels of glycine has been linked to health-promoting effects and increased life expectancy. High levels of methionine have been linked to increasing levels IGF-1 which can encourage cancer cell growth. It's important to maintain a healthy methionine-to-glycine ration by consuming glycine-rich foods.
High glycine “prime cuts” are attached to bones, cartilage, skin, organs, and all the other odd bits that now usually end up in pet food. Its’ a real shame as these cuts (especially liver) contains the highest levels of nutrients, in addition to glycine, that helps the body metabolise methionine, including vitamins B6, B12, folate, betaine, and choline. Another reason why the type and quality of the meat you eat are essential to health and longevity.
Protein is crucial in terms of our overall health, and there are many situations where either decreasing or increasing protein intake makes sense. One size does not fit all and macronutrient calculation based on height, weight, age and gender are a very general guide (check out if it fits your macros is not good enough) and do consider current health and lifestyle factors.
If you are an athlete and you are trying to train to improve sports performance (strength, spend, power and recovery) you are going to require significantly more protein than the average person doing minimal exercise. Athletes protein cravings aren’t just going to magically go up, they need to be aware of the additional training demands and adjust their intake protein accordingly.
Who require higher levels of protein intake?
Athletes with high training volumes:
Highly active people, those training more than 3 times per week, CrossFitters, competitive athletes, bodybuilders, anyone who’s doing a lot of glycolytic activity will perform, recovery and feel better on a high protein diet. Protein is the building blocks for lean muscle and plays an essential role in recovery and performance. There has been an ongoing body of research investigating post-workout protein intake for athletes of all sports. The International Society of Sports Nutrition states :
Vast research supports the contention that individuals engaged in regular exercise training require more dietary protein than sedentary individuals.
Protein intakes of 1.4 – 2.0 g/kg/day for physically active individuals is not only safe but may improve the training adaptations to exercise training.
When part of a balanced, nutrient-dense diet, protein intakes at this level are not detrimental to kidney function or bone metabolism in healthy, active persons.
While it is possible for physically active individuals to obtain their daily protein requirements through a varied, regular diet, supplemental protein in various forms are a practical way of ensuring adequate and quality protein intake for athletes.
Different types and quality of protein can affect amino acid bioavailability following protein supplementation. The superiority of one protein type over another in terms of optimising recovery and/or training adaptations remains to be convincingly demonstrated.
Appropriately timed protein intake is an important component of an overall exercise training program, essential for proper recovery, immune function, and the growth and maintenance of lean body mass.
Under certain circumstances, specific amino acid supplements, such as branched-chain amino acids (BCAA's), may improve exercise performance and recovery from exercise.
People aiming to lose weight:
Protein is the most important macronutrient when it comes to weight loss. There is plenty of research that supports a high protein diet ( of up to 35%+) which can be really effective for both short and longer-term weight loss. [5,6] Protein is the most satiating macronutrient, which means when you eat it you feel fuller for longer, and you are likely to naturally eat less and lose weight without trying.
One study took 39 adults and split into three groups . All three groups followed a specific diet and fitness regimen, the first was fed the recommended Regular Daily Amount (RDA) of protein, 0.8 grams of protein per kilogram of body weight. The second and third groups were fed 2xRDA amounts (1.6g/kg) and 3xRDA amounts (2.4g/kg), respectively. Those eating the greater-than-RDA amounts of protein lost the most fat mass and maintained the most fat-free lean muscle mass.
Two separate studies [9,10] supported this and showed that those eating a high protein diet lost 3.3 kilograms more body fat compared to a high-carbohydrate-eating group.
People with metabolic issues & blood sugar:
Protein stabilised blood sugar levels and has been shown to have a beneficial impact on a wide range of metabolic, cardiovascular, and inflammatory markers like C-reactive protein. A high protein breakfast tends to set the tone for the day and improve blood sugar regulation throughout the entire day. [11,12]
People who are under a lot of stress:
high levels of stress can increase allostatic load (wear and tear that stress causes in the body). Allostatic load leads to lean muscle tissue breakdown. Studies show that high cortisol (stress hormone) blunts the desire for protein-rich foods and increases cravings for high-carb, high-fat foods that are very rewarding. Protein, especially collagen, are important in rebuilding tissue and can be crucial for those who going through stress and anxiety. 
If you’re under chronic stress, or you are over the age of 50, your ability to make stomach acid can be impacted. Why is this important? If you have low stomach acid, you’re going to feel fuller for longer and you might not feel like eating protein because the digestion of protein requires good levels of stomach acid. Your ability to digest and absorb nutrients form your diet is impacted and this can quickly lead to deficiencies, disease and chronic illness.
People chronically ill and the elderly:
Muscle atrophy can be a problem for the chronically ill and the elderly. High protein intake can help reduce that muscle breakdown. . Strength is a predictor of life expectancy and hence maintaining muscle mass is critical to longevity.
We should always be aiming to get out nutrients from whole food whenever possible. Whole foods have a number of other beneficial co-factors and enzymes that help us to digest and absorb whatever nutrient we’re going for, and so that’s always the recommendation.
Protein supplements can be useful for those who need higher intakes of protein, the above list. It’s not something we would recommend for everybody as protein powder is processed and does not offer the same benefits as protein from real whole food. Protein powders also come with a high risk of food sensitivities and can often cause digestive issues if overused. There is no reason to be using a protein shake as a meal replacement, always eat real whole sources for your meals. A protein supplement should be seen as a supplement to a healthy diet. For more information on protein powders check out the article what is the best protein supplement for athletes.
How much protein do you need?
As we said, there is no one-size-fits-all approach in terms of a diet that works for everybody, we recommend consuming between 20-35% of calories from protein each day.
The higher end (30–35%) would be for aggressive weight loss, metabolic problems, and people doing extreme training
The middle end (25–30%) for athletes and people training at moderate to vigorous intensity
The lower end (20–25%) for the elderly, chronically ill, and people under a lot of stress.
That said, these are just general guidelines and we suggest you experiment through the entire range to see what works best for you and your health goals.
This is quite possibly much more protein than you’re eating now, even if you’re following a Paleo diet. Let’s look at some examples using the ranges below:
Our protein intake should spread out across the day and not simply eaten at one big meal. We would recommend eating between 40-65g (147-263cals) of protein per each main meal (breakfast, lunch and dinner) depending on your goals. Most people can benefit greatly from eating the right amount of protein for breakfast, we will talk about this more in a future blog post:
Long-Term Effects of High-Protein Diets on Renal Function, Kamper AL, Strandgaard S,2017
Changes in Kidney Function Do Not Differ between Healthy Adults Consuming Higher- Compared with Lower- or Normal-Protein Diets: A Systematic Review and Meta-Analysis. Devries MC, Sithamparapillai A, Brimble KS, Banfield L, Morton RW, Phillips SM. 2018
Low-carbohydrate, high-protein diets may reduce both tumor growth rates and cancer risk, American Association for Cancer Research, 2011
A Low Carbohydrate, High Protein Diet Slows Tumor Growth and Prevents Cancer Initiation, Victor W. Ho, et al, 2010
Effect of a high-protein, high-monounsaturated fat weight loss diet on glycemic control and lipid levels in type 2 diabetes, Parker B, Noakes M, Luscombe N, Clifton P., 2002
Effects of high-protein diets on body weight, glycaemic control, blood lipids and blood pressure in type 2 diabetes: meta-analysis of randomised controlled trials., Dong JY, Zhang ZL, Wang PY, Qin LQ., 2013
High protein diets decrease total and abdominal fat and improve CVD risk profile in overweight and obese men and women with elevated triacylglycerol., Clifton PM, Bastiaans K, Keogh JB., 2009
Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials.Wycherley TP, Moran LJ, Clifton PM, Noakes M, Brinkworth GD, 2012
Randomized trial on protein vs carbohydrate in ad libitum fat reduced diet for the treatment of obesity, Skov AR, Toubro S, Rønn B, Holm L, Astrup A. 1999
An increase in dietary protein improves the blood glucose response in persons with type 2 diabetes, Mary C Gannon, et al. 2003
Consuming high-protein breakfasts helps women maintain glucose control, University of Missouri-Columbia. 2014
International Society of Sports Nutrition position stand: protein and exercise, Bill Campbell, et al, 2007
Protecting muscle mass and function in older adults during bed rest, Kirk L. English, 2012
Protective and damaging effects of stress mediators: central role of the brain, Bruce S. McEwen, 2006