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High Protein Diets: Are They Healthy or Harmful?
PROTEIN IS EVERYWHERE NOW. From bars and shakes to high-protein snacks and an endless amount of content telling you to shoot for high-aggressive protein targets like 1g/lb bodyweight.
However, while some of the most well-published researchers are warning that high protein diets could actually increase the risk of disease and that there is no evidence that excess protein is beneficial, the answer isn't simply "high protein is good" or "high protein is bad". The answer lies somewhere in between the two extremes. The answer is based upon the age of the individual, their protein-related goals, and their source of protein.
Why Some Experts Are Warning Against High-Protein Diets
Some of the loudest warnings about high-protein diets are being sounded by Dr. Valter Longo. While he has many reasons for sounding these alarms, one of the primary reasons is based on a multitude of different types of data, including:
- Population Studies
- Lab Research
- Clinical Trials
- Observations of Long-Lived Communities
One of his most-cited studies followed over 6,000 adults 50+ for 18 years. During that time the participants were divided into three categories: low-protein, medium-protein, and high-protein.
Individuals in the high-protein category (those in the 50-65 year-old range) experienced:
- a 74% higher all-cause mortality rate compared to individuals in the low-protein category;
- more than four times the risk of dying from cancer.
Data such as that will make most people question whether a high-protein diet is truly worth the potential risks.
Biological Reasons Why This May Occur
The biological basis behind why this might happen is rooted in how nutrients influence cellular processes. Nutrient abundance sends a "growth" signal. Lower calories and lower protein send a "repair" signal.
Protein intake affects growth pathways, specifically mTOR, a central regulator of cell growth and metabolism. Amino acids send strong signals to mTOR. Leucine in particular sends a very strong signal to mTOR.
When amino acids are present in abundance, the body interprets this as a "grow" signal. When amino acids are less available, the body interprets this as a "maintain/repair" signal.
Cancer is uncontrolled cellular growth. Therefore, when the body is consistently in a growth-promoting state, it may theoretically facilitate cancer progression in vulnerable populations.
Numerous animal studies have demonstrated that high protein intake can promote cancer growth, supporting this concern.
Important Caveats: Protein Source & Age
Protein source is critical
Dr. Longo emphasizes that the concern is not protein in general, but rather specific amino acid profiles and growth signals that are more heavily activated by certain sources.
In Dr. Longo's aforementioned study, the negative impacts of high protein were primarily attributed to animal protein. Plant protein showed no similar risk profile.
Other large datasets have also indicated that protein from legumes, beans, and nuts is often associated with favorable outcomes whereas protein from red meat and processed meats are associated with adverse outcomes.
Age is also relevant
The negative association between high protein and cancer mortality observed in Dr. Longo's analysis primarily occurred in subjects under 65. Older adults experienced increased cancer mortality with low protein intake.
These findings indicate that older adults may require higher amounts of protein to prevent frailty, unintentional weight loss, and loss of muscle mass.
The Other Side of the Coin: Muscle Loss
While protein is primarily related to longevity theory, it is also related to preventing muscle loss.
Muscle loss begins earlier than most individuals expect and accelerates with age. Muscle loss is not solely due to a gradual loss of muscle. Researchers are increasingly describing a "catabolic crisis" pattern.
During catabolic crises, illness, bed rest, and/or a decrease in physical activity results in rapid muscle loss that does not return to normal. Over time, repeated episodes result in significant decreases in function.
Muscle loss results in decreased mobility, increased risk of falls, and lower quality of life.
Therefore, a critical question is: is the recommended minimum of 0.8g/kg/day adequate for older adults?
Many professional organizations agree that it is not. Recommendations for older adults include:
- 1.0 to 1.2g/kg/day for healthy older adults
Evidence supports the recommendations. One study examined adults aged 70-79 and determined that those consuming approximately 1.1g/kg/day experienced 40% less lean body mass loss over three years compared to those consuming approximately 0.8g/kg/day.
Maximizing Muscle Gain
Resistance Training and Protein Intake
Protein intake helps maximize muscle gain through resistance training. However, benefits plateau at higher intakes.
Earlier studies suggested that benefits peaked at approximately 1.6g/kg/day. More recent studies suggest that most of the benefit is achieved at approximately 1.3g/kg/day.
Benefits above 1.3g/kg/day are generally small for most individuals.
This is an important finding. It indicates that many individuals who are attempting to achieve extremely high protein targets are achieving relatively small additional benefits relative to the effort required.
For those interested in maximizing muscle gains, please see resistance training and healthy aging.
Protein and Weight Management
Protein also significantly contributes to satiety and fat loss.
Studies that compare higher protein diets to standard protein diets, with equal caloric intakes, have demonstrated:
- significantly greater fat loss;
- preservation of greater amounts of lean body mass;
- increased feelings of fullness;
- increased compliance.
Weight loss is often associated with a degree of muscle loss. Higher protein intake helps minimize the loss of muscle.
In a study comparing standard protein diets to high protein diets, the standard protein diets resulted in nearly twice as much lean mass loss as high protein diets during a calorie deficit, despite the fact that both groups exhibited similar amounts of total weight loss.
Kidney Health
Concerns regarding kidney health are commonly raised with respect to high protein intake, especially in individuals with chronic kidney disease.
Traditionally, clinicians have advised against high protein intake in advanced stages of kidney disease. However, new data presents a more nuanced view. Newer data suggests that higher protein intake in mild-moderate kidney disease is associated with improved survival rates.
Again, this is not a blanket statement. Individuals with documented kidney disease should consult with their clinician prior to establishing a high protein regimen.
The Middle Ground
Based on considerations of muscle preservation, weight management, and long term health risks, a reasonable middle ground exists.
A reasonable target for many adults would be:
- approximately 1.2g of protein per kg of ideal body weight per day.
This represents a level of protein intake that exceeds the minimal recommendation, but does not represent the extreme upper limit of 1.6g/kg/day that many advocates recommend. Additionally, this level of protein intake aligns with the notion that the largest muscle and body composition changes occur at approximately 1.3g/kg/day.
Most Importantly: Choose Better Protein Sources
It appears that much of the mortality data that is problematic appears to be influenced by consumption of animal protein, specifically red and processed meats and some dairy-based patterns.
Plant-based proteins are generally associated with lower mortality. Fatty fish is generally associated with favorable outcomes. Lean animal proteins can be a part of a healthy diet as part of a larger dietary pattern. This also aligns with broader dietary principles covered in healthy eating made simple.
A practical strategy is:
- emphasize legumes, beans, lentils, tofu, tempeh, nuts, and seeds;
- utilize fatty fish if you consume animal products;
- limit red and processed meats;
- select lean cuts if you choose to consume meat.
Conclusion
High protein diets are neither inherently good nor bad.
- High levels of protein intake may pose risks to certain subpopulations, particularly younger middle-aged individuals, in the absence of a clear need for the protein.
- Low levels of protein intake, particularly in older adults, may contribute to the development of frailty and muscle wasting.
- For many adults, a protein intake target of approximately 1.2g/kg/day represents a reasonable middle ground.
Ultimately, protein intake should serve to support your health, not control it. The focus should not be on achieving the maximum possible protein intake, but on achieving a protein intake target that preserves muscle, facilitates metabolic function, and is part of a healthy dietary pattern.