Sales of foods with “protein” on the label are skyrocketing, and new product launches of high-protein foods are soaring (Stagnito Media 2013). American shoppers want more protein in everything from cereals to snack foods, but in a society where protein intake is already adequate, are consumers getting too much of a good thing?
Nutrition and fitness professionals trumpeting the weight-loss and muscle-building benefits of dietary protein are instrumental in educating consumers hungry for information about the type, amount and timing needed for optimal health. The latest protein research stresses that the degree of physical activity is a key factor in determining protein needs.
Protein for Life
Protein comes from the Greek word protos, meaning first. Nearly every biological process in the body depends on protein, which is an essential structural component in all living cells. The human body is about 16% protein; nearly half of that is found in muscle, and the rest is incorporated in skin, connective tissues, blood, enzymes, hormones and immune cells. Body protein stores are constantly being broken down and rebuilt, a process that depends on adequate dietary protein.
Dietary protein contains a mixture of amino acids that form the building blocks of protein. When we ingest protein, gastric enzymes convert it into strings of amino acids called peptides. Protein and peptides are further enzymatically digested in the small intestine, with rendered amino acids rapidly absorbed into the portal circulation. From the liver, amino acids are shuttled throughout the body to supply muscle, blood and other tissues with the components needed to build, maintain and repair body proteins.
There are 20 amino acids that form proteins when linked together. Nine of these are called essential amino acids (EAAs) because they must be supplied via food. Protein tissue construction can proceed only if all amino acids are available; proteins can’t be formed if any of the EAAs are missing. EAAs are not stored for very long, so we need a fresh supply every day (CDC 2013).
Animal foods provide all nine EAAs and are dubbed “high-quality proteins.” Plants lack one or more EAAs and are considered incomplete proteins. Vegans, who shun animal products, must combine plant sources to create complementary proteins that deliver all EAAs (CDC 2013).
“Consumers are looking beyond animal sources of protein to meet their daily needs,” said Mangala D’Sa, brand director of Grape-Nuts® and Great Grains cereals at Post®. One of her products—Great Grains Protein Blend Honey, Oats & Seeds—includes pumpkin seeds, almonds, sunflower and cracked flaxseeds, all of which, she said, are natural sources of protein.
Protein: A Dietary Dynamo
Why do people lose more weight eating high-protein diets? Dietary protein is unique among the macronutrients in its ability to reduce fat and body mass weight while preserving muscle and boosting energy expenditure. Three key characteristics exclusive to protein explain why:
First, protein is the most satisfying of all the macronutrients (Rebello et al. 2013). High-protein meals dampen appetite by creating a sense of fullness triggered by a milieu of hormones (Belza et al. 2013). Feeling full reduces intake and promotes weight loss, but the type and quality of protein appear to influence this effect. Satiety is a driving factor of high-protein food sales (Kreger, Lee & Lee 2012).
“Many consumers are adopting the habit of starting the day with a protein-packed breakfast to keep them satisfied,” D’Sa said. At the urging of customers craving more early-morning protein, Post relaunched its Grape-Nuts cereal in 2013 with an upgrade to 8 grams of protein per serving.
Second, high-protein diets help shed pounds because protein digestion and metabolism are energetically expensive processes. Both carbohydrate and protein provide the same amount of energy, 4 kilocalories per gram, but it takes about 25% more energy to process protein (Acheson et al. 2011). This means that energy expenditure and the thermic effect of food (the energy cost to metabolize a protein meal) are higher for protein, and so more calories are burned.
Third, when people shed pounds, calorie-burning lean body mass is typically lost. Overweight dieters are more likely to shed fat instead of muscle if they follow a high-protein, calorie-restricted diet. Adequate dietary protein at the expense of fat or carbohydrate calories preserves and stimulates new muscle tissue (Westerterp-Plantegna, Lemmens & Westerterp 2012). Adding exercise enhances this effect (Tipton 2011).
How Much Protein Is Enough?
Most Americans get plenty of protein. The Institute of Medicine recommends 10%-35% of total calories from protein (IOM 2002); American adults on average consume nearly 15% of their caloric needs from protein (USDA Agricultural Research Service 2012). While the definition of a “high”-protein diet varies, it is generally defined as drawing 25%-30% of calories from protein (Westerterp-Plantegna 2007).
Protein recommendations vary based on activity level and health status. An absolute amount of protein, 0.8 g-1.2 g per kilogram of body weight, is necessary to promote satiety and weight loss. Higher amounts are beneficial to body composition (Westerterp-Plantegna, Lemmens & Westerterp 2012).
For healthy, sedentary adults, the recommended dietary allowance of 0.8 g/kg of body weight is adequate to preserve and repair body tissues (that’s about 54 g for someone who weighs 150 pounds). However, 1.2-1.7 g/kg is suggested for endurance athletes (AND 2013a), and 1.4-1.8 g/kg is recommended for strength athletes (AND 2013b).
For healthy adults, 2 g/kg is the maximum usable amount of protein, and there is no benefit in consuming more (Tipton 2011).
A Balancing Act
Excessive protein rarely causes problems for healthy people. However, protein exceeding 45% of total calories will trigger nausea, weakness and diarrhea. For some, too much protein taxes kidney function and may cause painful kidney stones and dehydration (Tipton 2011). Excessive protein may also leech valuable bone-strengthening calcium from the body, increasing the risk of osteoporosis (Bonjour 2011).
Too little dietary protein causes tissue breakdown, brittle hair and impaired immunity. Protein deficiency in the United States is rare, but older adults, those with certain chronic diseases like cancer, and individuals recovering from bed rest or injury have higher protein needs (English & Paddon-Jones 2010).
Protein for Muscle Mass
Resistance exercise increases muscle synthesis when all EAAs are available within 24-48 hours following exercise (Rennie & Tipton 2000). Free amino acids from whey appear in the circulation within 15-30 minutes of ingestion, while amino acids derived from intact proteins, such as lean beef, can take up to 100 minutes to peak (Symons et al. 2011).
Symons et al. (2009) reported that aging does not diminish muscle synthesis in healthy older adults after a high-quality protein meal and a bout of resistance exercise. Thirty grams of high-quality protein eaten within 60 minutes of leg extension repetitions boosted mixed muscle fraction synthesis by 108% within 5 hours following the exercise bout. Similarly, a meta-analysis of 22 studies by Cermak et al. (2012) revealed that protein supplementation significantly augmented muscle mass and strength in both younger and older subjects who participated in more than 6 weeks of resistance exercise.
Older adults experience a blunted increase in muscle protein synthesis following meals containing less than 15 g of protein, though moderate amounts of protein (30 g) enhance muscle synthesis in young and old alike (Symons et al. 2011). A minimum amount of high-quality protein spread throughout the day in increments of 25-30 g per meal optimizes muscle synthesis (Symons et al. 2009). Older adults tend to consume most of their protein at the evening meal and should be encouraged to eat protein at each meal (Berner et al. 2013).
Regardless of age, it’s critical to add proteins that contain high levels of leucine, a key stimulator of muscle synthesis. Addition of supplemental leucine, or its metabolite beta-hydroxy beta-methylbutyrate (HMB), improves or normalizes muscle protein synthesis (Rieu et al. 2006; Wilson, Wilson & Manninen 2008).
People engaged in regular exercise training require more dietary protein than sedentary individuals. The International Society for Sports Nutrition position paper on protein suggests that protein intakes of 1.4-2.0 g/kg/day for physically active people are safe and may improve training (Campbell et al. 2007). Protein at this level doesn’t harm kidney function or bone metabolism in healthy people. Active individuals can get plenty of protein in a regular diet, but supplemental protein ensures adequate intake of quality protein.
The superiority of one protein over another remains unproved. Timing of protein intake is important to overall training and essential for recovery, growth and maintenance of muscle. Under certain circumstances, specific amino acid supplements, such as branched-chain amino acids, may improve exercise performance and recovery from exercise (Campbell et al. 2007).
Finding the Right Mix
Protein is essential to life and good health, but most Americans get plenty without adding protein-packed snacks. The weight loss benefits of high-protein foods has them flying off store shelves, creating a halo effect that can blind consumers to the reality that they might not need a lot more protein in their diets. Fitness professionals who have an understanding of their clients’ activity levels, health status and allergies can recommend the right type and amount of protein for optimal well-being.
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