Lemon divides physical activity into two broad categories, heavy resistance exercise and endurance exercise. For resistance exercise, Lemon cites several studies that have approached this subject from different aspects. Fern (1991) compared body mass gains using 3.3 versus 1.3 grams of protein per kilogram of bodyweight per day. After 4 weeks, the 3.3 group had larger gains. Meredith et al. (1992) found the addition of 23 grams of protein per day enhanced muscle gains. Two studies are also cited that held individuals at the RDA for protein and found negative nitrogen balance after engaging in strength training (Lemon et al., 1992, Tarnopolsky et al., 1992). The Tarnopolsky study also used protein intakes of 1.4 and 2.4 grams per kilogram per day with no difference in protein synthesis between the 1.4 and 2.4.

Lemon summarizes this work as follows, "These studies indicate that the RDA (which was determined using subjects who were essentially sedentary) is insufficient for individuals who are involved in a heavy resistance training program." Lemon goes on to show linear regression analysis to arrive at a protein intake of 1.7 - 1.8 grams of protein per kilogram of bodyweight per day to maintain nitrogen balance while working out with weights.

For endurance exercise, the issue of protein requirement is a little different. While muscle growth is not likely to occur, increased protein needs do occur for two other reasons. The first is applicable to strength training as well which is that physical activity increases protein turnover and requires a greater daily intake to sustain itself. The second aspect for endurance is that protein is burned for fuel along with fats and carbs. Both exercise intensity (Babij et al., 1983) and exercise duration (Haralambie and Berg, 1976) influence protein utilization. For exercise intensity, the protein contribution is roughly linear. For duration, the utilization of protein becomes substantial after about 60 minutes.

One complicating factor is that certain amino acids are utilized to a greater extent than other. Branched chain amino acids (BCAAs) for example, feed into the TCA cycle directly for energy production. Thus, with 2 hours of moderate intensity exercise (55% VO2max), 86% of the daily requirement for leucine (a BCAA) can be burned (Evans et al., 1983). With protein, loss of one amino acid can render any other excess protein nonusable for general protein synthesis. Combining the results of several studies (Gontzea, 1974; Tarnopolsky et al., 1988; Brouns et al., 1989; Friedman and Lemon, 1989; Meredith et al., 1989) results in the recommendation of 1.2 - 1.4 grams of protein per kilogram of bodyweight per day for endurance athletes.

One final note for those pursuing a low carb diet with exercise can be found in an article, Lemon and Mullin (1980). Previous nitrogen balance studies have relied on measuring nitrogen excretion by adding up nitrogen in urine and stool. One major source for error in physically active people is that nitrogen is also lost through sweat. Clearly, sweating occurs more readily in physically active individuals. In this study, sweat urea nitrogen loss was measured in carb loaded verses carb depleted individuals during exercise at 61% VO2max. At rest, nitrogen losses in sweat were almost undetectable. In the carb depleted individuals, the sweat urea nitrogen loss was more than doubled that of carb loaded individuals performing the same activity. This suggests that a reduced carb diet would utilize more protein during endurance activities.

Lemon recommends 1.2 - 1.4 grams per kilogram per day for endurance work and 1.7 - 1.8 grams per kilogram per day for strength. So the question arises, how do these values mesh with the advice of carb reduction diets? Sears uses a sliding scale of 0.5 - 1.0 grams of protein per pound of lean body mass per day. One difference is that Sears is using lean body mass, while Lemon and other researchers use total mass. Sears' specification of lean body mass appears sound for two reasons; first, physiologically, lean body mass should be the major source of metabolism with fatty tissue contributing very little; second, most of the studies cited here were done in relatively lean individuals so that kilogram of bodyweight versus kilogram of lean body mass are going to be in close agreement.

The first column lists the activity level. The second column lists the Lemon values of grams of protein per kilogram of bodyweight per day. The third column converts this value to per pound of bodyweight. The fourth column converts column three to lean body weight by assuming a typical body fat percentage of 20%. What is clear is that the activity factors of Sears, 0.5 - 1.0, are well in line with research study results. In fact, given the increased protein utilization by carb depleted individuals, one could reasonably argue for increasing protein intakes above Sears' guidelines, but there is little data available on the in between carb loaded versus carb depleted to make specific recommendations.

A final point to be noted is that many criticisms of Zone style eating are based on the erroneous assumption that 30% of calories from protein is too much protein. This is clearly misguided thinking. Protein needs of the body are determined by absolute amounts, not percentages. The only way to determine if 30% is too much or too little is to know the total caloric intake. For example, a diet consisting of only 25 grams of protein per day is 100% protein, but is clearly deficient in terms of protein needs; while a diet of 5000 calories with 10% protein is still consuming 125 grams of protein per day which is about double the current RDA recommendations. The percentage of protein is meaningless in terms of protein needs.