Will I get leaner and stronger if I drink protein supplements?
Protein intake is just one part of the nitrogen balance equation, along with total calories (energy), carbohydrate intake and, of course, exercise. "The greatest amount of muscle growth seems to occur when protein intake is 1.7-1.8 g protein/kg bodyweight/day (10%-15% of nutrient intake), energy intake is sufficient (that is, weight is not lost) and carbohydrate intake is high (60%-65% of nutrient intake)," state Ann Snyder and Jay Naik in Nutrition for Sport & Exercise (Berning and Steen, Aspen Publications, 1998). That is, if you're eating enough calories and carbohydrate, your dietary protein will be used for muscle-related needs. But if you're on a strict low-carb diet, chances are that some of that protein will be converted into fuel - a very inefficient use of dietary protein.

What's the moral of the story? Protein supplements can definitely help you in your quest to reach your daily protein quota, which according to Snyder and Naik equals about 0.8 gram per pound of bodyweight, but you have to also make sure you're eating enough total calories and carbohydrate.

What type of protein is best: whey, soy, casein, egg, or a combination of these?
Before you get too worried about which protein to choose, here's some food for thought: "At the normal levels of protein that fitness enthusiasts consume, the total amount is far more important than the source," says Wright. Your best efforts should be concentrated on getting 0.7-0.8 gram of protein per pound of bodyweight.

Regarding which is best, protein quality is determined by two major factors: how well the protein satisfies amino-acid requirements and the digestibility of the protein. A high-quality protein contains all the essential (also called indispensable) amino acids in adequate amounts. Digestibility is important because not all the protein in a selected source can be digested and absorbed by the body. These two criteria are combined in the Protein Digestibility-Corrected Amino Acid Score (PD-CAAS), which is basically a rating system for proteins. Other protein-quality measurement tools include Biological Value and Protein Efficiency Ratio. The major protein sources (whey, casein, milk protein, egg white and soy) used in most commercial protein powders all score highly on each of these measures. If you're eating a wide variety of foods and getting protein from many sources, you don't need to be too concerned with protein quality.

Which is better, whey or casein?
Regular milk contains a mixture of both whey and casein, which possess different properties that make them desirable for use in protein powders. A landmark 1997 study by Yves Boirie et al. found that whey protein (WP) and casein (CAS) operated differently in the body. Regarding timing, whey (a "fast" protein) moved more quickly through the body than did casein (a "slow" protein). The other major factor studied was protein synthesis vs. protein breakdown. While whey was used quickly for protein synthesis, casein was better at preventing protein breakdown (catabolism). "Whole-body protein breakdown was inhibited by 34% after CAS ingestion but not after WP ingestion," stated the authors.

This research led many to choose "fast" whey after a workout and "slow" casein throughout the day. Yet if you eat food with your protein drink (or blend the powder with milk, yogurt or fruit), the rates of digestion and absorption will change slightly.

What's the benefit of soy protein?
If you're simply concerned with protein intake, any of the major protein sources will be sufficient, as soy, whey and egg are all similar in terms of protein quality. Soy is sometimes desirable for other reasons, primarily isoflavone content. Isoflavones are phytoestrogens that are valued for their beneficial effects on the cardiovascular and skeletal systems. Like most other soy products, protein powders can be a good source of isoflavones.

"The proteins vary quite a bit in their isoflavone content, but the average for soy protein isolates is about 1 mg per gram of protein," states Mark Messina, PhD, soy expert and associate professor of nutrition at Loma Linda University in California. "Many products that are geared more toward the recent interest in the health effects of soy have 2 mg/g." (One such product is SUPRO soy protein, which is manufactured by Protein Technologies International. You'll find SUPRO listed as a protein source in some powders.) Tofu, soymilk and most other soy products are good sources of isoflavones, with an average of 3 mg/g of protein (the exception are soy burgers made from soy protein concentrate). Messina cautions that women with a history of breast cancer should speak to their doctor before consuming soy.

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