For most Chinese people, protein intake is definitely not enough. The traditional Chinese breakfast is all kinds of noodles, porridge, steamed buns, and some fried carbohydrates, cakes, etc. These are high in carbohydrates and high in fat. The protein is often only eggs or milk, and not everyone will eat it in the morning. At noon and at night, there is generally still meat, but depending on the situation, there may not be a lot.
Generally, only fitness people or nutrition-conscious people pay attention to protein intake. Because exercise increases the body’s need for protein, people who exercise will consume more protein than people who are sedentary. This makes some people wonder, is it good to eat so much protein? Is there any harm?
The most common concerns associated with high-protein diets are kidney damage, bone loss, and cancer. So whether high-protein diets are related to these, let’s see what the research says.
High protein diet and kidney damage
One of the most common misconceptions in nutrition science is that a high-protein diet increases the workload of the kidneys , which over time can cause damage and eventually lead to kidney failure. However, this is only a concern for people with kidney disease.
For example, a 2003 study looked at changes in glomerular filtration rate (GFR) in patients with pre-existing kidney disease over an 11-year period [1]. The findings found an association between increased protein and decreased kidney function, suggesting that high protein intake may accelerate kidney damage.
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PS: The glomerular filtration rate (GFR) is a test used to assess how well the kidneys are working. Glomeruli are small filters in the kidneys that use to filter waste products from the blood.
The statement that “protein is bad for the kidneys” stems from the idea that long-term high protein intake can damage these filters, leading to kidney failure.
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However, the above-mentioned literature also looked at the effects of high protein intake in 1135 women with healthy kidneys and found no association between changes in GFR and protein intake.
A systematic review and meta-analysis in 2018[2] observed high protein intake (20% of total calories) in over 1300 subjects and low protein intake (5% of total calories). The researchers concluded:
Two studies published in recent years by Antonio et al. both observed extremely high protein intake. In the first study [4], 48 subjects consumed either 2.3 g/kg or 3.4 g/kg of protein for 8 weeks. At the end of the study, no effect was found on kidney function.
In the second study [5], subjects ingested 2.5-3.32g/kg of protein per day for one year, and the researchers found no effect on blood lipids and liver and kidney function.
So, As long as you are a healthy adult and your kidneys are fine, then you don’t need to worry about high protein intake affecting your kidneys.
Does a high-protein diet cause bone loss?
A long time ago, metabolic balance studies found that when people eat more protein, calcium in their urine increases. The theory is that high protein intake increases blood acidity, causing the body to take calcium from the bones to balance pH. Over time, the loss of calcium can lead to bone loss.
However, the newer study calls into question these earlier studies because of the unscientific testing methods. For example, the meta-analysis by Fenton et al. concluded that there is no high-quality evidence from metabolic balance studies that increasing dietary acid load promotes bone mineral loss or osteoporosis. Changes in urinary calcium cannot accurately reflect calcium balance [6].
Furthermore, if high-protein diets do lead to bone loss, then we should see an increased risk of fractures in people consuming high-protein diets. But in fact, the result is quite the opposite.
For example, Kerstetter et al. observed data from 1882 women aged 50 and over and found that higher protein intake was associated with higher total bone mineral density in the femoral head [7].
Kerstetter et al., 2000.
A 2017 systematic review by the National Osteoporosis Foundation and meta-analysis looking at 16 randomized controlled trials and 20 prospective cohort studies, they found that high protein intake had no adverse effect on bone health[8].
A 2018 expert consensus document approved by the European Society for the Clinical and Economics of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases and the International Osteoporosis Foundation found that protein intake was higher than the RDA (0.8g/kg) may help reduce bone loss and hip fracture risk. The same review also noted that low protein intake is associated with a higher risk of bone health than high protein intake [9].
Speaking of fractures, there is some evidence that In patients who have just recovered from a hip fracture, a higher intake of protein (both calcium and vitamin D) may help speed recovery [10].
So in general, a high-protein diet does not lead to bone loss, and it actually reduces the risk of fractures. This becomes even more important as we age, which is why older adults need to focus more on protein intake.
Protein and Cancer
First, we need to figure out one thing. When a lot of people say “high protein diets cause cancer,” they actually mean red meat.
This is very important. Because of the same protein, white meat, fish, dairy and plant proteins are all healthy and inversely associated with cancer and mortality. Even the link between red meat and cancer has been limited by some studies so we can’t draw firm conclusions.
The first problem is that studies linking red meat to cancer are observational—researchers review data and try to find a link, while observational studies can only point to potential Correlation, not causation.
While observational studies can help us start a good conversation leading to better controlled trials, due to logistical, cost and ethical is not always possible, which means that other factors can interfere with observational studies.
For example, a 2012 study found that red meat consumption was associated with increased overall mortality, cardiovascular disease, and cancer mortality [11] . But the researchers noted that people with higher red meat intake were less likely to participate in physical activity and were more likely to be current smokers, drinkers and people with higher BMIs. Also, higher red meat intake was associated with higher total energy intake, while lower intake of whole grains, vegetables and fruits.
Similarly, a meta-analysis published in the European Journal of Cancer looked at the association between red and processed meat intake and breast cancer. Subjects with breast cancer were less physically active, more likely to have previously smoked, had higher BMI, and had lower vegetable intake [12].
So, is it just because of red meat, or is red meat an underlying factor in an unhealthy lifestyle? It has been shown that people who live a healthy lifestyle, whether they are vegetarian or not, live longer than those who are not vegetarian[13,14]. Additionally, some studies do not differentiate between unprocessed and processed meats. For example, hot dogs and lean beef. If that doesn’t differentiate, it’s hard to tell if it’s a red meat problem or a certain type of red meat.
Evaluation of diet is another issue. Most studies used a 24-hour recall questionnaire. We all know that not only are most people bad at reporting exactly how much they actually eat, but that a day’s food intake isn’t always representative of a person’s usual eating habits.
Finally, associations using experimental studies (ie, animal models) do not always apply to humans.
First, the experimental models used meat or meat components at levels far higher than those found in the human diet, even in cultures with high meat intake. in this way. Take heme iron, a substance present in meat that is associated with an increased risk of several cancers, and is used in experimental models 9-22 times higher than in the average human diet [ 15].
Second, the experimental model used a pure food that does not contain fruits and vegetables, which have many benefits.
Even the World Health Organization has classified red meat as “probably carcinogenic” to humans, acknowledging that this is based on limited evidence and other explanations, Such as randomness, bias, or confounding factors that cannot be excluded.
So, red meat is not definitive, but proper intake may not be a problem with an overall healthy diet. Finally, remember that your overall lifestyle has a greater impact on cancer risk than single foods.
Summary
For healthy adults, there is no need to worry about the health effects of high protein intake. Moreover, we recommend that fitness people increase their protein intake, not brainless crazy intake, but a little more than sedentary people.
While increasing your protein intake, you still need to pay attention to your overall diet structure, eat more fresh vegetables and fruits, and have a balanced diet.