Research Review

Martin WF et. al. Dietary protein intake and renal function. Nutr Metab (Lond). 2005 Sep 20;2:25.

Recent trends in weight loss diets have led to a substantial increase in protein intake by individuals. As a result, the safety of habitually consuming dietary protein in excess of recommended intakes has been questioned. In particular, there is concern that high protein intake may promote renal damage by chronically increasing glomerular pressure and hyperfiltration. There is, however, a serious question as to whether there is significant evidence to support this relationship in healthy individuals. In fact, some studies suggest that hyperfiltration, the purported mechanism for renal damage, is a normal adaptive mechanism that occurs in response to several physiological conditions. This paper reviews the available evidence that increased dietary protein intake is a health concern in terms of the potential to initiate or promote renal disease. While protein restriction may be appropriate for treatment of existing kidney disease, we find no significant evidence for a detrimental effect of high protein intakes on kidney function in healthy persons after centuries of a high protein Western diet.

My comments: For years, anybody who has eaten a high protein diet (which I'm going to define here as greater than 1.5 g/kg, most athletes eat in the realm of 2 g/kg or higher for reference) are bad for the kidneys, will cause kidney damage, etc.

However, there's been very little data to support the idea. So where did the idea come from? Probably from the following: it's been known for years that individuals with pre-existing kidney problems need to reduce their protein intake and it's fairly clear that high protein intakes do hasten kidney damage when there is a pre-existing problem. Somehow this got reversed from 'people with damaged kidneys need to eat less protein' to 'high-protein intakes will damage your kidneys.'

There are some additional theoretical reasons for this belief as well. For example, in both dogs and mice, increased protein intake causes renal hypertrophy (growth of the kidneys) and increased filtration but whether or not this causes pathological changes in the kidney is unknown. The paper points out that, during pregnancy, filtration can increase by 65% but this doesn't appear to be a risk factor for the development of kidney disease. It has been suggested that the increase in kidney size and filtration may simply be an adaptation to the increased protein intake.

In addition and somewhat more directly, the paper references recent studies of high-protein diets for both weight loss and athletes, which have found no negative impact on kidney function (despite some of the subjects in the weight loss trials being at risk for kidney disease). Simply put, there is no data to suggest that high protein intakes are a cause of kidney damage or dysfunction. Of course, no research has examined the very high end of protein intakes, 3-4 g/kg (1.5-2 g/lb) that are sometimes eaten by bodybuilders. At least in the range of 1.5-1.9 g/kg, there is no evidence to suggest a risk of causing kidney problems.

Finally, the paper looks at the issue of kidney stones, concluding that, at best, high protein can be a problem for individuals with a condition predisposing them towards kidney stones. Basically, you need to have a pre-existing dysfunction for protein to become a problem.

The paper concludes by saying "Although excessive protein intake remains a health concern in individuals with pre-existing renal disease, the literature lacks a significant research demonstrating a link between protein intake and the initiation or progression of renal disease in healthy individuals. More importantly, evidence suggests that protein-induced changes in renal function are likely an adaptive mechanism well within the functional limits of a healthy kidney. Without question, long-term studies are needed to clarify the scant evidence currently available regarding this relationship. At present, there is not sufficient proof to warrant public health directives aimed at restricting dietary protein intake in healthy individuals for the purpose of preserving renal function."

For anybody who would like to read the full paper, the full text is available free here.

Feature Article:

Energy Density

I want to look at a concept that sort of integrates the concepts of calories, nutrients and food intake. That concept is energy density. Simply defined, energy density refers to the caloric content in a given weight of food. Looking at the values for protein, carbs and fat (4,4, and 9 cal per gram respectively), it seems obvious to conclude that protein and carbs have the same energy density while fat has nearly twice the energy density.

This fact is frequently interpreted in one of two ways depending on whether authors are pro- or against-fat. Pro-fat authors will point out that fat contains twice as many calories as carbohydrates, hence it can provide more energy on a gram basis (I'll discuss this issue later on). Anti-fat authors blame high-caloric intakes (and hence obesity) on a high-fat intake because of its high energy density

But just looking at the energy density of the individual macronutrients can be misleading for the reasons discussed last chapter: few foods contain pure amounts of a given nutrient. Even if they did, it would be unusual for someone to eat a single food at a time; rather, humans eat a mixture of foods and that affects energy density. More relevant to the real world is the number of calories found in a given weight of food. This is because, depending on food source, a given weight (say 100 grams) of food may contain non-digestible fiber, air, water and any other number of compounds.

Soup is an easy to understand example, because it is mostly water content. So say you make a soup of potatoes, vegetables, ground beef, vegetable oil or what have you. Although each of the individual foods falls somewhere on the energy density scale, the overall energy density of the soup will likely be low because of the high water content. Or as another example, compare a meal containing 2 cups of pasta to 1 cup of pasta and 1 cup of vegetables; the second meal would contain far less calories in the same amount of food because of the very low energy-density of the vegetables. Essentially, the low energy-density food dilutes whatever it's combined with.

As another example, take your typical 100 gram baked potato which contains about 25 grams of carbohydrates. Contrast that to 100 grams of table sugar which, of course, contains 100 grams of carbohydrates. In both cases we're looking at 100 grams of food, but the caloric content of the two are drastically different (100 calories vs. 400 calories). Obviously the baked potato has a lower energy density (25 grams carbohydrate/100 grams food) than the table sugar. Of course, compared to 100 grams of pure fat (containing 900 calories), the fat will still have the highest energy density.

As another example, 2 cups of grapes contain about 100 calories, 2 cups of raisins (dried grapes) might contain nearly 800. This is because the raisins have had most of their water and air content removed, concentrating their calories into a much smaller volume. Or compare an apple (which contains air, water, fiber) to fruit juice; the fruit juice will contain more calories for a given weight than the apple. This is why both fruit juices and dried fruit tend to be shitty diet food compared to whole fruits, they are far more calorie concentrated.

Energy density becomes important for a number of reasons especially when you start talking about fullness, appetite and weight loss. Some research suggests that humans eat a constant weight of food so foods that are higher in energy density are easier to overeat than low energy density foods. Even if this isn't entirely the case, high energy density foods tend to make it easier to overconsume calories compared to low energy-density equivalents.

Simply put, foods with a low energy density will contain a relatively small number of calories with high-bulk. Vegetables, fruits and other unrefined carbohydrates typically have a low energy density although even that's not always the case as mentioned above. Foods with a high energy density will contain a large number of calories in a relatively small amount of food. This generally includes high-fat foods but can also include highly refined carbohydrates. I want to look at that issue in a little more detail.

It looks at first glance that high fat foods will always be more energy dense than similar amounts of carbohydrates or protein and that fact has been used as part of the campaign to lower dietary fat to help with the obesity problem. But is this always the case, are high-fat foods always higher energy density?

Let's take our baked potato example, containing about 25 grams of carbohydrate in a 100 gram potato. So it contains about 100 calories/100 grams. Let's say we add 10 grams of fat in the form of butter (making anti-fat crusaders cringe) to the potato which adds 90 calories. Our potato/butter combination contains 190 calories in 110 grams of food. Now let's contrast this 110 grams of candy and let's say it contains 100 grams of sugar, or 400 calories. So the baked potato/butter combination contains 190 calories/110 grams of food while the candy contains 400 calories/100 grams of food. Despite being 'high-fat', the potato-butter combination has a lower energy density than the low-fat food its being compared to.

As a very real world example, we might consider the Mediterranean diet. Despite having a fairly high fat content (as percentage), the overall diet is still relatively low energy density because of the preponderance of fresh fruits and vegetables. Despite having a high fat content, the Mediterranean diet has an overall low energy density because of the other foods that are present in such abundance.

As I mentioned above, one of the reasons that fat is so often blamed for its role in causing obesity is its high energy density. This is obviously true if you're talking about pure fat (which few people eat) and it's generally true that high fat foods have a high energy density. This difference is especially prevalent if they are compared to low-fat unrefined carbohydrate foods likes fruits, vegetables and unrefined grains. You know, the foods that nobody really eats but that anti-fat crusaders think people are eating.

In conjunction with this, a low-fat diet isn't automatically a low energy-density diet. Many highly refined high-carbohydrate foods have a high energy density because the water, air, fiber, etc. has been removed. More and more, food companies have brought low-fat/high-carbohydrate but also high energy density foods to market. Even diet staples such as pasta can have a surprisingly large number of calories in a fairly small volume. Such foods may be low (or even no) fat but still have a very high energy density. This not only makes them easy to overconsume but also means that they can contribute a rather large number of calories to the diet without providing much bulk.

To say it again, a high-fat diet isn't automatically a high energy density diet any more than a low-fat diet is automatically a low-energy density diet. The types and amounts of other foods in the diet play a major role. This isn't to say that an excessive fat intake isn't contributing to the energy density (or caloric content) of the modern diet; of course it is. Dietary fat simply isn't the only factor contributing to the problem (a point I'll come back to again and again).

So which is better? You may be thinking after the above discussion that choosing a low energy-density diet is always superior. In the case of weight/fat loss and overall health, this is probably generally true. Certainly if you don't want to have to worry so much about tracking or counting calories, choosing low-energy density foods (read: lots of high water content foods such as fruits and vegetables) is an easy way to limit caloric intake while eating a large volume of food.

However, optimal dietary choices is not always as simple as choosing low energy density foods. There are times, that I'll discuss in later articles and newsletters, where high energy density foods may be preferred. Athletes with high caloric requirements may not be able to eat enough if they choose low-energy density foods. There are other times that high energy-density foods may be superior. Post-workout, for example, it may be impossible to get sufficient calories and/or carbohydrates if you pick low-energy density foods; this is especially true for those athletes who simply aren't hungry after training.

Questions and Answers

Q:Would it be beneficial in any way if I use high reps low weights for lower body and low rep heavy weights for upper body while dieting for fat loss? I currently have very thick muscular legs. I don't mind at all sacrificing muscle on lower body (I would prefer to lose some muscle to be honest) , however I would like to maintain upper body muscle while losing fat. What are your thoughts taking into account that higher reps may be more beneficial in losing fat. Would muscle be lost also in upper body irrespective of going higher reps for only lower body? or most muscle loss would be from lower body parts?

A: Given that situation, I would expect any muscle loss to come primarily from the lower body since you had removed the heavy tension stimulus needed to prevent muscle loss on the diet. As long as you kept training the upper body heavily, I wouldn't expect you to lose muscle mass in your upper body under those conditions.

Q: I have your UD2.0 and Flexible Dieting books. Both are really great reads, and I think I learned a lot. I am a 29 y.o. female, and weigh 92-94 lbs, 16% fat by DEXA. I also have low bone mineral density, so I'm lighter than I look.

My question is this: is it necessary or best, at my weight/body fat, etc., for me to do UD2.0 in order to lose fat (esp. my saddle bags) and retain what little lean mass I have. Or should I still be able lose fat and retain muscle just with combining a slight caloric deficit (11-12*BW?) and regular refeeds? (Yes, I'm afraid of the depletion workouts).

A: Unfortunately, this is kind of an impossible question to answer. It really all comes down to how much muscle you tend to lose on more traditional diets (with refeeds). The simple fact is that non-cyclical diets work just fine for many people; there's no de facto reason to use one unless you tend to really lose muscle badly on a non-cyclical diet.

Quite in fact, I will always recommend that someone use the simplest diet that is effective for them to meet their goals; while I do think that most people will benefit from properly planned refeeds, doing a diet as involved as the UD2 may simply not be necessary. Try the simpler approach first, move to more complex approaches only when the simpler stuff stops working effectively

So I'd say this: if you don't lose muscle on a traditional diet, you should do just fine with a moderate deficit, heavy training and the occasional refeed. If you do tend to lose a lot of muscle when you diet, UD2 may be worth trying

Q: Lyle, Please put to rest the question of how much muscle can be build in say a year, by both the average person, and say a 50 year old female, lifting what for her is heavy (60# chest press) while on deficient calories to lose fat. I'm thinking 'Nada'. I'm just tired of hearing the same ole 'stay off the scale' the scale lies ... weight gain could be muscle! Not. If I stayed off the scale, I'd pork up for sure, it's taken me 6 months to take off the excess 20 pounds I put on last year, now using the FD to maintain for 10 days before I restart dieting, and while yes I see some definition in my back, and arms ... finally, I really don't expect to gain much muscle over the course of the next couple of years ... maintaining what I've got would be nice, I'll continue to work at it

A: On average, I'd say a typical young-ish male trainee might put on 20-25 lbs of LBM in their first year of training, maybe half that the second year, and half again the third. Beyond that, further gains tend to be pretty slow in coming.

Of course, this assumes a semi-intelligent training program and that they eat sufficiently, neither of which is a safe assumption. It also depends on what rate they are willing to put fat on. Of course, you can always find exceptions to this, folks who put on a tremendous amount more (who are typically underweight to begin with) and folks put on less. Consider the above averages

The typical female might put on half those numbers with decent training. So 10-12 lbs in their first year, half again in their second, half again in their third

An older female clearly isn't going to gain nearly that much, especially in a caloric deficit. However, it's not unheard of for beginning trainees to gain some muscle while losing fat at the same time. Years ago, working with several older women, I would typically see 3-4 lbs muscle gained and 5-10 lbs of fat lost over the first 8 weeks of training.

At the end of the day, I'm not sure worrying about the exact numbers is going to be that valuable, there's just too much variability. If you focus on making strength gains (which are important for overall health and function, not to mention bone density; important for older women), you should gain whatever muscle you're going to gain. It sounds like you're making progress towards your goals, I suspect that's more important in the long-run than anything else

I do want to mention that it looks like post-workout nutrition timing may be more important as we age in terms of gaining muscle mass; in one study (in elderly men), delaying a post-workout protein/carb drink (10 grams protein, 7 grams carbs, 3 grams fat) by 2 hours after training eliminated the gains in muscle mass compared to a drink consumed immediately afterwards.