There are many options for diets aimed at reducing body fat, but the difference between them lies only in the different ratios of macronutrients (proteins, fats, and carbohydrates) and their amount. Today we take a look at the available scientific publications on the efficacy and safety of a high-protein diet.
What’s High-Protein Diet?
High protein diets (HPDs) also have different and subjective definitions. They are generally defined as diets with protein intakes reaching or exceeding 25% of the total calories per day, or 1.2 to 1.6 g protein/kg.
Research papers by Lymon et al. showed that protein consumed twice the recommended intake (1.6 g / kg) was many times higher than the norm set at 0.8 g / kg in terms of maintaining lean muscle mass and reducing fat.
However, Pasyakos et al. found that a protein dosage three times the norm (2.4 g / kg) did not preserve muscle mass significantly more than a dosage twice the norm.
More recently, Longland et al. found that on a low-calorie diet that included high-intensity interval sprints and resistance training, a protein intake of 2.4 g / kg even led to an increase in muscle mass by 1.2 kg and a loss of fat by 4.8 kg, while the 1.2 g / kg dose only resulted in muscle retention and less fat loss at 3.5 kg.
Longland et al. is distinguished by the unique methodological quality of the study in terms of the assessment of body composition and nutritional control of the participants.
The latter were provided with a pre-prepared all necessary daily ration of food and drinks.
Complementing this is the study by Asiero et al. on the distribution of proteins during the day: 4-6 meals a day, more than 30% of the caloric intake of food falls on protein, the total consumption is more than 1.4 g / kg/day.
This work demonstrated the superiority of this method over conventional, low-protein / low-frequency diets for improving body composition in energy-deficient states.
Protein Has the Greatest Thermal Effect
The thermal effect of food is understood as the amount of energy that the body spends on its digestion and absorption.
For protein, this value reaches 30% of the energy value of the consumed portion. That is, having consumed 40 grams of protein, we theoretically get 160 kcal (1 gram of protein = 4 kcal), but actually less, since 50 kcal is spent on assimilating this amount.
Given this fact, it should come as no surprise that higher protein intake often does not increase fat stores or create barriers to reducing them.
In addition, protein is the most saturating macronutrient. It is followed by carbohydrates and then fats.
The consistency of virtually all recent meta-analyzes supports the benefit of higher protein intake for reducing total body weight, fat mass, waist circumference, and keeping muscle mass under energy.
Antonio et al. recently initiated a number of studies that, based on the amount of protein consumed, hyper-protein diets can be considered.
Initially, dietary protein supplementation at 4.4 g / kg for eight weeks in resistance exercising subjects did not significantly alter body composition compared to maintenance energy control conditions and 1.8 g / kg protein.
It is noteworthy that such a high portion of protein created an energy surplus of ~ 800 kcal/day, but this did not lead to additional weight gain.
The ensuing 8-week study involved individuals who were also doing resistance training according to an established periodic protocol.
The high protein (HP) group consumed 3.4 g / kg, while the normal protein (NP) group consumed 2.3 g / kg.
HP and NP showed significant gains in muscle mass (1.5 kg in both groups). But a noticeably greater decrease in fat mass occurred in the HP group compared to NP (1.6 and 0.3 kg, respectively).
This is interesting because, in the HP group, the increase in caloric intake from protein from baseline increased more significantly (374 kcal), while the increase in calories in the NP group was not statistically significant (103 kcal).
Another 8-week crossover study in trained subjects compared protein intake at 3.3 g versus 2.6 g / kg/day.
There were no significant differences in body composition and strength performance, despite significantly higher calorie intake for HP compared to NP.
The important thing here is that there was no significant increase in fat mass from excess energy derived from proteins.
This study also addressed the health concerns of long-term high protein intake (3-4 times the recommended intake) by demonstrating no adverse effects on the full list of clinical markers measured, including the complete metabolic panel and blood lipid profile.
An inpatient metabolic ward study by Bray et al. compared hypercaloric (surplus) conditions for 8 weeks with protein intake of 5% (LP), 15% (NP), and 25% (HP) of total energy.
All three groups gained total body weight, but the LP group lost 0.7 kg of muscle mass. And the NP and HP groups gained 2.87 and 3.98 kg of lean muscle, respectively.
All three groups increased body fat by an average of 3.51 kg, with no significant difference between groups.
These results are at odds with the observations of Antonio et al., in which the participants gained little or no fat due to the protein-induced surplus.
However, in addition to the tighter control and oversight inherent in the metabolic ward environment, participants in the Bray et al. were not exercising and remained inactive during the entire observation period.
The subjects of Antonio et al. were physically fit, had intense resistance training, and could have an advantage in macronutrient oxidation and nutrient distribution.
Thus, the energy surplus created by high protein intake is potentially less dangerous in terms of increasing body fat, mainly for athletes who train with weights but not physically inactive people.
As for the fate of excess calories from high doses of protein, which for some reason did not lead to an increase in fat mass, here the scientific world suggests that this happens due to a number of reasons:
- higher thermal effect from eating food (an increase in the cost of its assimilation),
- increased thermogenesis of everyday activity (more energy is spent on all our movements and movements),
- increased thermal effect of physical exertion,
- increased excretion of fecal energy,
- reduced consumption of other macronutrients by increasing satiety and suppressing hepatic lipogenesis (fat synthesis in the liver).
At the moment, high-protein diets are the most popular, as they have proven their effectiveness not only in clinical settings but also in real practice.
Among the athletes involved with weights, such diets are followed by all without exception.
How to Preserve Muscle Mass?
In this regard, the question arises whether there are any parameters of high-protein diets that can already be adopted by those who not only want to lose weight but also strive to preserve the muscle mass gained by training.
Yes, there are.
Let’s turn to the recommendations from a systematic review and concurrent doctoral dissertation on dietary protein and macronutrient intake by bodybuilders on a calorie deficit diet from Eric Helms, a scientist, and active bodybuilder.
“… Protein intake should be set in the range of 1.8-2.7 g / kg for total body weight or 2.3-3.1 g / kg for lean body weight. The upper limits of this range are prescribed when the athlete already has a low body fat percentage and when his training program is based on a high volume of loads (that is, the less fat remains in us and the more we exercise, the more relevant it will be to increase the amount of protein). Fat intake should be in the 15-30% range of total calorie intake, with the remaining calories from carbohydrates. If performance decreases during exercise, it may be beneficial to reduce the percentage of calories from dietary fat within this range in favor of a higher proportion of carbohydrates …”
And again about the safety of high amounts of protein.
“Several review articles show that there is no controlled scientific evidence that increased protein intake poses any health risks in healthy, exercising athletes. The positions voiced by reputable international and state institutions / regulatory bodies also testify in favor of the fact that fears for personal health are secondary to the consumption of increased amounts of protein and are unfounded. A series of controlled studies, spanning periods of up to one year, during which protein intakes of up to 2.5-3.3 g / kg/day in healthy people doing strength training consistently show that increased protein intake does not have a detrimental effect on blood lipids or kidney markers and liver function. “
A weight-loss high-protein diet, in which protein accounts for 30% of the energy, works better than a traditional weight loss diet, in which protein is only 20% of the daily energy supply.
In addition, it is as good for the cardiovascular system as the traditional low-calorie diet, even if followed for a year.
This conclusion was made by Australian researchers from the University of South Australia in a study involving 120 men with large overweight.
Effects of High-Protein Diet on Weight Loss
There is considerable evidence that weight loss occurs faster with more protein in the diet. In addition, diets high in protein will help maintain muscle mass. However, it is not yet entirely clear whether there are long-term negative health effects from a high-protein diet.
Research methodology for the impact of a high-protein diet on health in a study published by Australians in the Nutrition & Diabetes journal, obese men (mean age 50) were put on a 1,700 kcal/day diet that they had to follow for a year.
Half of the men followed the traditional diet (HC): 20% of their energy was obtained from proteins (88 g in total), 58% from carbohydrates (198 g in total), 17% fat (51 g in total, 14 g saturated).
The other half of the men were put on a high-protein diet for weight loss (HP).
The energy in this diet was distributed differently: 35% from protein (total 143g), 40% from carbohydrates (total 135g), the remaining 25% were fat (total 53g, saturated 14g).
Both groups lost about the same amount of weight in the year the experiment lasted.
But men on a high-protein diet lost more fat and maintained lean body mass. The differences were statistically significant.
Since lean mass is closely correlated with resting energy expenditure and accounts for ~ 60-70% of daily energy expenditure, the smaller decrease in lean mass observed in the HP group may have implications for achieving sustained weight control after returning to an ad libitum diet (no limit).
In addition, because skeletal muscle represents the largest mass of insulin-dependent tissues, mitigating the effects of lean mass in the HP group may also provide metabolic health benefits, especially in this study population, which is at increased risk of developing type 2 diabetes and/or cardiovascular disease due to a large percentage of body fat.
The health status of men in both groups became higher, which usually always happens with a decrease in excess weight.
Their blood pressure dropped, good HDL cholesterol went up, blood sugar and insulin levels went down, as did triglycerides, bad LDL cholesterol, and an inflammation marker, CRP.
High-Protein Diet Reduces Weight and Has Beneficial Effects on Health
“To conclude, in overweight and obese men, both high-protein and high-carbohydrate diets reduce body weight and improve cardiometabolic risk factors,” the researchers write.
“Following a high-protein diet was more effective in improving body composition compared to a high-carbohydrate diet.”
High-Protein Diet Helps Maintain Muscle Mass
A protein-rich diet for weight loss, in which thirty percent of energy comes from protein, works better than a traditional weight loss diet, in which protein is only twenty percent of the energy supply.
Plus, a high-protein diet is just as good for your cardiovascular system as a traditional weight loss diet – even if you stick with it for a year.
Australian researchers from the University of South Australia came to this conclusion in a human study of 68 overweight men.
There is quite a lot of evidence that you lose weight faster when you consume more protein and that a high protein diet also helps maintain muscle mass.
The aim of the present study was to investigate the long-term effects of two low-fat, hypocaloric diets with different carbohydrate-to-protein ratios (HP vs HC) on body composition and cardiometabolic health in overweight and obese men.
In a study published by Australians in the Nutrition & Diabetes journal, physically inactive obese men (mean age 50) were on a 1,700 calorie diet daily for a year.
As a result, they gradually lost weight. Half of the men (33 people) followed a traditional diet: 20% of their energy came from protein, and 50% from carbohydrates (high-carbohydrate).
The other half of the men (35 people) were on a high-protein diet for weight loss. The energy in this diet was 30 percent protein and 35 percent carbohydrate.
How Body Quality Changes With a High-Protein Diet
Both groups lost about the same amount of weight in the year that the experiment lasted – about 11% of their baseline. But men who were on a high-protein diet lost more fat and retained more muscle mass. The differences were statistically significant.
The loss of muscle mass in the high-protein group was 21% of the total weight loss, versus 35% in the high-carb group.
Cardiometabolic Risk Factors and Kidney Function
At 52 weeks, both groups showed similar increases in good HDL cholesterol and decreases in total cholesterol, low-density lipoprotein cholesterol, triglycerides, glucose, insulin, blood pressure, and C-reactive protein.
The creatinine clearance, which characterizes renal function, did not change in any of the groups during the intervention.
Overall, changes in body weight at 52 weeks correlated with changes in triglycerides, HDL cholesterol, glucose, and insulin.
Scientists’ Conclusion on the Effects of a High-Protein Diet
“To sum up, in overweight and obese men, both high-protein and high-carbohydrate diets reduce body weight and improve cardiometabolic risk factors,” the researchers write.
“Consuming a high-protein diet was more effective in improving body composition compared to a high-carb diet.”
This study further confirms that energy balance is paramount when it comes to the weight change.
And when it comes to changing body composition, the composition of the diet becomes equally important.
The energy function of proteins is limited in comparison with carbohydrates and fats. And, if in studies, manipulating the ratio of carbohydrates and fats with an equal amount of protein and total calories does not show a significant difference, then manipulating the proportion of protein in the diet relative to other nutrients always has noticeable consequences.
- A moderate-protein diet produces sustained weight loss and long-term changes in body composition and blood lipids in obese adults. Layman DK, Evans EM, Erickson D, Seyler J, Weber J, Bagshaw D, Griel A, Psota T, Kris-Etherton P. J Nutr. 2009 Mar; 139(3):514-21
- A Systematic Review of Dietary Protein During Caloric Restriction in Resistance Trained Lean Athletes: A Case for Higher Intakes. Helms, E. (2013). Exploring protein and macronutrient intakes in lean bodybuilders during caloric restriction (Doctoral dissertation, AUT University).
- Comparison of the effects of 52 weeks weight loss with either a high-protein or high-carbohydrate diet on body composition and cardiometabolic risk factors in overweight and obese males. Nutr Diabetes. 2012 Aug 13;2: e40.
- Dietary protein and exercise have additive effects on body composition during weight loss in adult women. Layman DK, Evans E, Baum JI, Seyler J, Erickson DJ, Boileau RA. J Nutr. 2005 Aug; 135(8):1903-10.
- Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial. Bray GA, Smith SR, de Jonge L, Xie H, Rood J, Martin CK, Most M, Brock C, Mancuso S, Redman LM JAMA. 2012 Jan 4; 307(1):47-55.
- Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. Longland TM, Oikawa SY, Mitchell CJ, Devries MC, Phillips SM. Am J Clin Nutr. 2016 Mar; 103(3):738-46
- Protein-Pacing from Food or Supplementation Improves Physical Performance in Overweight Men and Women: The PRISE 2 Study. Arciero PJ, Edmonds RC, Bunsawat K, Gentile CL, Ketcham C, Darin C, Renna M, Zheng Q, Zhang JZ, Ormsbee MJ Nutrients. 2016 May 11; 8(5):. High Protein Diet Has No Harmful Effects: A One-Year Crossover Study in Resistance-Trained Males. Antonio J, Ellerbroek A, Silver T, Vargas L, Tamayo A, Buehn R, Peacock CA. J Nutr Metab. 2016; 2016():9104792.
- Review Dietary approaches to the treatment of obesity. Makris A, Foster GD Psychiatr Clin North Am. 2011 Dec; 34(4):813-27.
- T P Wycherley, G D Brinkworth, P M Clifton & M Noakes. Nutr Diabetes. 2012 Aug 13;2: e40.
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