There is much debate around this hot topic and justifiably so. To the common person with little nutritional knowledge, carbs and fats are what make you put on weight right? Protein takes longer to break down and keeps you fuller for longer and therefore it must be the answer. Unfortunately, it is not that simple. Before we delve into this discussion lets take a few steps backwards and define the key components.
What are Proteins
Amino acids are the building blocks of protein and are made up of carbon, hydrogen, oxygen, nitrogen and sulphur.
Percentage-wise, 43% of our body’s protein is in our muscle, 15% in our skin and 16% in our blood.
Amino acids transform from primary to secondary to tertiary and then finally to its quaternary structure, where it forms a protein.
Proteins have many functions in our bodies. They form bodily structures and frameworks, part of our immune system, digestive enzymes, part of our skin hair and nails, blood clotting and more.
What Are the Recommended Dietary Intakes (RDIs) for Protein for Males and Females?
Important to note as well that all animal-based proteins e.g. meat, eggs and dairy contain all amino acids, whereas with plant-based proteins one needs to eat the correct combination of foods in order to obtain all amino acids. According to the Handbook of Clinical Nutrition and Dietetics women aged 19-70 should be consuming 46g/day, and males aged 19-70 should be consuming 64g/day.
For children, the recommendations are lower, and for women who are pregnant or lactating recommendations are higher. The RDI for fibre is 30g for males and 25g for females.
Overall, it is recommended that one’s protein consumption should comprise 15-25% of one’s daily diet, fat should comprise 20-35% and carbohydrate should comprise 45-65%. Clinically, a diet becomes ‘high protein’ when one is consuming >1.2g/kg/day but particularly >1.5g/kg/day.
How Much Protein Is in the Food I Eat?
The table below illustrates how many grams of protein is contained in 100g of high protein foods.
|Food Source||Amount of Protein (g)/ 100g||Food Source||Amount of Protein (g)/100g|
|Bacon, middle, fried, fat removed||30.5||Lamb||18.8|
|Barramundi, grilled or baked||27.3||Lentil||24.2|
|Bean, haricot, dry||21.9||Mixed nut and seed mix||21.6|
|Bean, soy, dry, cooked||13.5||Mussels||19.2|
|Brie cheese||19.3||Salmon, baked or grilled||24.3|
|Cottage cheese||15.2||Seeds, Sesame||22.2|
|Feta cheese||17.8||Seeds, Pumpkin||24.4|
|Chicken fillet||21.3||Seeds, Sunflower||22.7|
Branched-Chain Amino Acids
Branched-chain amino acids are essential amino acids that make up 30% of our muscles. They include leucine, isoleucine and valine.
Essential amino acids are those that the body is unable to make itself and therefore needs to be obtained from the diet. They include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Branched-chain amino acids are not metabolised in the liver, rather they go straight to the muscle where they are either metabolised and used as fuel for energy or are built into new protein.
Protein and Weight Loss
There are three main mechanisms that could simplistically satisfy the argument that a high protein diet is conducive to weight loss.
More energy is expended metabolising protein than is spent metabolising carbohydrates or fats. 20-30% of the energy derived from protein foods is actually used in the metabolism of them, compared to carbohydrates and fats which use approximately 5% and 15% respectively.
Because protein takes longer to break down in the gut, it stays in your stomach for longer which in turn delays gastric emptying and thus increases satiety.
3. Decreased energy intake:
As a result of increased satiety, one experiences a decrease in energy intake. In other words, because you stay fuller for longer, you don’t feel the need to eat as often and therefore your total energy (caloric) intake decreases.
Since muscle burns more calories than fat, maintaining muscle could help make it easier to create a calorie deficit which is required for weight-loss.
To put this in context, muscle burns ~12kcal/kg/day compared to fat at ~4kcal/kg/day, while at rest. This isn’t going to translate to a huge difference, but it is worth being aware of.
High protein diets do NOT cause issues with kidney function unless people already have pre-existing issues. This is one of the most common myths out there. It is so commonly accepted among health professionals that a lot have never actually looked at the evidence and found out that there is no need for concern for those who are otherwise health.
For those who DO have issues with kidney function, it is best to refer to the evidence-based practice guidelines for the nutritional management of chronic kidney disease. For stage 3 chronic kidney disease the guidelines recommend 0.75-1g/kg IBW protein. It’s also worth noting that going too low protein, in that case, is also an issue since protein-energy malnutrition also has adverse effects on kidney function.
Another common concern some people hear is that higher protein intakes reduce bone mineral density.
This is based on the acid-ash hypothesis that suggests that animal proteins are acidic, so can disrupt the bodies pH. Since pH needs to be regulated within a specific target range, the theory is that the body needs to counterbalance this acidic state by increasing the availability of alkaline minerals, such as calcium which is stored in the bones.
Based on this theory, a chronic need to restore pH to its normal levels could result in bone mineral density decreases due to this need to take calcium out of the blood. This concept is also supported by evidence that diets higher in animal protein sources are associated with greater urinary calcium losses.
While this does make theoretical sense, it is still only one of the mechanisms involved in bone mineral density.
One specific example of the flaws in that logic is that although the urinary losses of calcium are increased, it appears like a large percentage of that is not coming from the bones, but actually due to an increase in the calcium that is absorbed from foods and increased overall calcium availability.
There are also other factors such as the fact that a large percentage of the makeup of bones actually comes directly from protein as well.
The evidence appears to be quite clear that high protein diets do not directly lead to decreases in bone mineral density. Meanwhile, low intakes of protein have been associated with fractures and low bone mineral density.
Regardless, it is still important to focus on other aspects of bone health though such as calcium, vitamin D, magnesium, potassium and vitamin K though.
Some of the Evidence in Regards to Weight Loss
Three of the more interesting randomised control trial studies that have been conducted found the following results:
1. Due A, Toubroi S, Skov AR, Astrup A. 2004. Effect of normal-fat diets, either medium or high protein, on body weight in overweight subjects: a randomised 1-year trial.
– High protein diet (30% of energy) achieved greater weight loss over 6 months in comparison to the moderate protein group (25% of energy). The difference was 9.6kg vs 5.9kg.
– By 12-months, both groups had regained a little bit of weight, which is common in weight-loss studies. Almost all studies with long durations suggest that the majority of participants show a trend towards regaining weight. By 24-months the weight-loss appeared to be maintained, but there was a relatively high dropout rate.
– Even at 12-months, the higher protein group had a 10% greater reduction in intra-abdominal adipose tissue.
– It’s also worth noting that the difference between 25% and 30% of energy coming from protein isn’t that large and probably not what people think of when they consider “high protein” in comparison to moderate protein intake.
2. Clifton PM, Keogh JB and Noakes M. 2008. Long-term effects of a high-protein weight-loss diet.
– This study trialled both a high protein and a high carbohydrate diet. Results showed that the average weight loss was 4.6kg and 4.4kg respectively after the 64-week period.
– A significant increase in HDL (good) cholesterol in the high protein group, insulin secretion reduced in both groups and glucose decreased in both groups. There was also a decrease in triglycerides and LDL (bad) cholesterol in both groups. Iron and B12 significantly increased in the high protein group.
– At 64-weeks it was however noted that higher reported protein intake was linked with more weight-loss, even though the different groups that people were placed into didn’t demonstrate this.
3. Sacks et al. 2009. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates.
– Weight loss of 6kg after 6 months was similar for all diets. This study showed a similar trend for weight being regained after 12 months. Only 23% of participants continued to lose weight post 12 months.
These studies amongst others indicate that weight loss may is relatively achievable in the short term, and protein intake may be a factor in this. It may also be helpful for contributing to maintaining that weight-loss.
However, weight loss is more often than not unable to be maintained in the long term. The majority of studies indicate that on average, people regain weight, regardless of which protocol is used. Higher protein intake might slightly increase the likelihood of maintaining weight loss, but it certainly isn’t the solution by itself.
Lauri is a student dietitian anticipating graduation in September of this year. Lauri is passionate about health and fitness and strives to embody the values of: everything in moderation, positive body image, lifestyle eating not dieting, as well as eradicating the war on carbs.