Question: You refer to “adequate protein intake” as important, but what do you consider adequate? In my case — calorie restriction of ~750-1000 kcals below BMR coupled with regular strength training? Is there a percentage of intake you consider ideal, and is it higher while dieting versus maintenance (to prevent muscle loss during times of restriction)?
Answer: The above question actually came through in the comments section of Exercise and Weight/Fat Loss: Part 2 and I thought it was important enough to address explicitly since it’s a place where I still see many mainstream diets and dieters making mistakes. It’s worth noting that bodybuilders and other strength athletes have been promoting higher protein intakes while dieting for decades and this is yet another place where modern science has ended up validating those beliefs many years after the fact.
The question of adequate protein under different conditions is one that has a long history of debate, the issue of maintenance requirements as well as protein intakes for athletes is still highly debated with science on both sides of the story (for details you can refer to The Protein Book).
With regards dieting specifically, this was a topic of much study in the 60’s and 70’s as researchers started looking past the simple issue of weight loss and into that of changes in body composition; the goal moved from weight loss per se to that of generating fat loss while minimizing lean body mass and muscle mass loss.
After much toing and froing and research had been done it was eventually found that a protein intake of about 1.5 g/kg of lean body mass (LBM; note that researchers actually used Ideal Body Weight but this is a rough proxy for LBM) was necessary to spare LBM losses in a non-training obese individual consuming low calories.
This is about double the DRI for protein (at 0.8 g/kg) at maintenance calories. So for an overweight individual at say 200 pounds and 30% body fat (this would give them an LBM of 140 lbs or 63 kg), that would be a protein intake of 95 grams of protein per day. Please note that this value is simply a minimum and dieters may still find that higher protein intakes are beneficial from a hunger blunting effect or what have you (see below).
In that context, I’d mention that at least one of the studies I referred to in Exercise and Weight/Fat Loss: Part 2 that found no benefit of resistance training gave something like 40 grams of protein to the subjects; far less than necessary or adequate. So it’s no surprise that no protein sparing effect of exercise was seen; the diet was inadequate in the first place.
It’s worth noting that more recent research supports further benefits of increased protein intakes while dieting, beyond simple lean body mass maintenance. Protein is the most filling nutrient (meaning that higher protein intakes tend to control hunger better) and studies have found that higher protein intakes can help to stabilize blood sugar levels while dieting which has benefits from both an energy level and appetite standpoint. Protein high in the amino acid leucine (with the dairy proteins whey and casein being the two proteins highest in leucine) seem to have extra benefit in this regard.
Now, as individuals get leaner, protein requirement tend to go up further for reasons discussed in other articles on this site. As well, regular training tends to further increase protein requirements. So lean athletes trying to lose fat while sparing lean body mass loss need even higher protein intakes than this. And we’ve known for decades now that caloric intake per se tends to impact on protein requirements; as caloric intake goes down, protein requirements go up. And vice versa.
While less data on this group is available, bodybuilders and athletes have long used a protein intake of 2.2 g/kg (1 g/lb) lean body mass as a generalized intake level and as folks get very lean, intakes of 3.3 g/kg (1.5 g/lb) of lean body mass may be required to stave off muscle loss while dieting. In some very extreme cases, such as the near protein only diet approach of my own Rapid Fat Loss Handbook even higher protein intakes may be required for very lean individuals.
So basically we have an intake continuum ranging from about 1.5 g/kg (0.68 g/lb) as a minimum for the obese non-training individual up to a high of around 3.3 g/kg (1.5 g/lb) of protein per pound of lean body mass for very lean heavily training athletes or bodybuilders with middle ground values being found in between those two extremes. You’ll note that I didn’t put any of those values in terms of percentages for reasons discussed in Diet Percentages: Part 1 and Diet Percentages: Part 2.
So that’s what I mean by ‘adequate protein on a diet’ when I use that phrase. It’s context dependent with the primary variables being body fat percentage (as this goes up, protein requirements go down), caloric intake (as caloric intake goes down, protein requirements go up and vice versa), and activity (with regular activity generally increasing protein requirements).