Protein is just one of the macronutrients we need as part of a healthy diet. There is a lot of focus on protein and its role in human health, but how much protein should a balanced diet contain per day?April 29, 2022 7:58 pm April 29, 2022 7:58 pm
The role of protein
Humans need protein for muscle development and overall good health. In fact, the word protein means “first”, from the Greek word protos. This reflects protein’s primary role in human nutrition. Protein is an essential macronutrient and we need it for muscle and tissue development along with various other roles in the body.
Athletes and bodybuilders consume higher amounts of protein compared to the average person. This is because muscle gains are a priority for them and protein plays a major role in muscle formation. However, the idea that the general population should also be consuming more protein is a misconception.
Advertisements for protein bars, powders and shakes all suggest that our protein intake from food alone isn’t enough. But is that truly the case? In reality, in developed countries, most people across all ages groups and genders are actually overconsuming protein.(1) So how much protein should a balanced diet contain per day?
How much are we consuming?
As previously stated, humans need protein for healthy muscle development and bone health. Many foods, from grains and cereals to meat, dairy, nuts, eggs and legumes, contain protein.
In the UK, the Reference Nutrient Intake (RNI) for protein for adults is 0.75g per kg of body weight per day. In other words, for a man and a woman weighing 75kg and 60kg, the RNI would be 56g/day and 45g/day respectively. RNIs are also set for children aged 0 to 10 years as well as for pregnant and breastfeeding individuals. Across all age groups in the UK, average protein intakes are higher than the recommended amounts.
The National Diet and Nutrition Survey (NDNS) found that in the UK, the largest contributor to protein intake is meat. Cereals and milk/milk products are in second place.The UK Government’s nutritional guidelines encourage the population to consume more legumes along with two servings of fish per week. Ideally you should consume one weekly portion of oily fish such as salmon, mackerel or sardines. With regards to red meat, the recommendation is to reduce your intake to a maximum of 70g per day (this includes both red and processed meats).
Moreover, protein intakes should be spread out across the day. In addition, the dietary guidelines published by the Department of Health recommend that protein intakes should not go beyond twice the recommended intake. However, there was insufficient data to establish a safe upper limit for protein intake.(2)
All protein is not created equal
The jury is still out regarding the ideal amount of protein required for optimal health. In addition, the role of high-protein diets in weight loss is still controversial. There are encouraging results in the short-term and little research available for the long-term effects of such diets.
However, not all protein is the same and we should consider the differences when thinking about our protein intake. In fact, many people believe that eating more protein means eating more meat. If you eat meat, along with dairy and eggs, these provide high-quality protein. However the same is true for many plant-sources of protein. In fact, whole grains, legumes, nuts and vegetables are all great sources of protein.
Moreover, we should consider protein as a macronutrient within a food as opposed to a nutrient in isolation. In fact, the other nutrients that you consume with the protein can be just as important as the protein itself. For example, you should primarily consume protein sources that are lower in saturated fats and highly refined carbohydrates. Moreover, it can be beneficial to consume protein sources that are also high in vitamins, minerals and fibre.
In addition, if you wish to increase your protein intake without gaining weight, you should cut back on other foods to maintain the same energy intake. The foods you choose to eat more of or cut back on can affect your health positively or negatively. For example, deciding to eat more plant-based protein sources instead of highly refined carbohydrates like white bread can benefit your health.
Protein and weight loss
Kathy McManus is the director of the Department of Nutrition at Brigham and Women’s Hospital, a Harvard-affiliated hospital. When it comes to protein intake, she suggests being picky about which types of protein you want to eat more of. In fact, she discourages her patients from increasing red meat let alone processed meat in order to boost their protein intake. Instead, if you are willing to integrate more fish into your diet, McManus supports the idea stating that it may be beneficial to your overall health.
In addition, many patients ask her if a high-protein diet is the secret to weight loss. Unsurprisingly her take on the matter is that you can’t expect a miracle solution just by adding one type of macronutrient to your diet. While trying a high-protein diet in the short-term can help some people achieve weight loss, the jury is still out on this topic. In fact, the evidence is still controversial. Some scientists swear by high protein diets for weight loss whereas others tout the benefits of more macronutrient balanced diets such as the mediterranean diet.(3)
“Resistance training and protein consumption act synergistically to build muscle mass if you consume protein pre or post workout.”
In 2003, a group of researchers conducted a meta-analysis to establish new and updated dietary guidelines for protein intake amongst healthy adults. In fact, to this day the most recent international dietary protein recommendations are from 1985. Indeed, it was in that year that the FAO/WHO/UNU Joint Expert Consultation published their dietary recommendations. According to these guidelines, how much protein should we consume per day as part of a balanced diet?
The researchers gathered data from published nitrogen balance studies in order to devise new protein recommendations. Nitrogen balance refers to the difference between nitrogen intake and loss reflecting gain or loss of total body protein. In fact, protein contains nitrogen and is our main source of nitrogen intake. If we consume more nitrogen (protein) than we lose, then we are in positive nitrogen balance, also known as anabolic. However, healthy adults normally maintain their lean body mass and protein mass is neither accumulated nor lost. This is known as nitrogen balance, where nitrogen (protein) intake is approximately equal to nitrogen losses. There are exceptions to this in the case of specific conditions. In cases of protein-energy malnutrition for example, we lose protein mass. Conversely, bodybuilders and athletes can increase their protein intake to accumulate protein mass.(4)
The researchers gathered data from 19 different studies including a total of 235 individuals. From this data, they estimated the recommended dietary allowance (RDA) to be 132mg N/kg/day. In addition, they estimated the median estimated average requirement (EAR) to be 105mg N/kg/day. Overall, the meta-analysis suggested new recommendations for dietary protein reference values for healthy adults. These were 105 (EAR) and 132 mg (RDA) N/kg/day respectively. These values correspond to 0.65 and 0.83g protein/kg/day respectively.
An exception for elderly people who may need more….
Although protein recommendations target the general healthy population, requirements for the elderly can be different. In fact, with age, sarcopenia can affect older adults. This is also known as muscle wastage. In fact, muscle mass typically decreases as we grow older. Sarcopenia leads to negative outcomes such as increased falls, frailty and ultimately mortality. Genetic and lifestyle factors can significantly influence this process.
A group of researchers conducted a systematic review and meta-analysis of observational studies. In this study they analysed the relationship between protein intake and physical function in the elderly. Older subjects with high (>1g/kg/day) and very high protein intakes (>1.2g/kg/day) showed superior physical functioning of the lower limbs faster and walking speed. In comparison, older adults with low protein intakes (<0.8g/kg/day) showed lower scores on these outcomes. Conversely, higher protein intakes did not affect handgrip strength or chair rise (measuring leg strength). Moreover, there was no significant difference between high and middle protein intake groups with regard to physical functioning.(5)
Overall, these findings suggest that protein guidelines for older adults may need to increase above current recommendations. However, we need large randomised control trials to ensure the safety of recommending high-protein diets for older adults.
Although the evidence is mixed
Interestingly, not all studies point to the same conclusion. In fact, another group of researchers conducted a systematic review and meta-analysis to investigate the relationship between frailty and protein intake in older adults. Frailty characterises the elderly who are at highest risk of negative outcomes including falls, disability, being admitted to hospital or requiring long-term care. The study included a total of 50,284 older adults from three different continents between 2006 and 2018. Results showed that a high protein intake was negatively associated with frailty in older adults.(6)
Overall, despite the mixed evidence, further larger studies are required to accurately determine if older adults should be following higher protein recommendations.
Increased requirements for athletes
Due to their increased energy expenditure and high lean muscle mass, athletes typically consume more protein than the average person. The International Society of Sports Nutrition (ISSN) holds a position with regard to protein intake for healthy active individuals. The ISSN states that intense exercise, in particular resistance/weight-bearing exercise, and protein intake both stimulate muscle protein synthesis. In fact, resistance training and protein consumption act synergistically to build muscle mass if you consume protein pre or post workout.(7)
For most healthy and active people, protein intakes between 1.4 and 2g protein/kg body weight/day is sufficient. Given this range, exercising individuals can build and maintain muscle mass through positive nitrogen balance. In addition, this intake range is aligned with the Acceptable Macronutrient Distribution Range as defined by the Institute of Medicine for protein.
Moreover, there is debate around the role of protein in athletic performance depending on the type of athletic activity (aerobic vs. resistance-based).
In practice, athletes whose goals are to gain muscle and strength typically consume more protein compared to endurance athletes. An example of this distinction is a weightlifter versus a marathon runner.
Resistance-based athletes consume such high amounts of protein because they believe it is required to build more muscle.
Athletes in particular require protein for more than just avoiding the risk of deficiency. In fact, protein for athletes may assist them in functioning at higher levels and adapting to their exercise regime.
Branched-chain amino acids and muscle protein synthesis
Researchers from the Exercise Metabolism Research Group at McMaster University in Canada published their consensus opinion regarding the role of protein in muscle synthesis. They postulate that leucine and potentially other branched-chain amino acids are particularly important when it comes to stimulating muscle protein synthesis (MPS). In addition, protein intakes between 1.3 and 1.8g/kg/day equally spread out across 3 to 4 meals throughout the day will enhance MPS.
Of course these recommendations can vary depending on the status of the athlete. In fact, more experienced athletes may require less protein, whilst athletes may need higher amounts during times of high intensity training. Moreover, during times of energy restriction when athletes are aiming for fat loss, extra protein consumption can help. In fact, intakes as high as 1.8 to 2g/kg/day may be helpful depending on the athlete’s calorie deficit.(8)
Overall, it seems that protein intakes vary widely between individuals and can be affected by multiple factors from gender and age to activity status. If you are unsure of how much protein you should be consuming per day as part of a balanced diet, speak to a registered dietitian who can provide a tailored plan for your individual needs.
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