New Review Paper by Yours Truly: High-Fat Dairy, Obesity, Metabolic Health and Cardiovascular Disease

My colleagues Drs. Mario Kratz, Ton Baars, and I just published a paper in the European Journal of Nutrition titled "The Relationship Between High-Fat Dairy Consumption and Obesity, Cardiovascular, and Metabolic Disease".  Mario is a nutrition researcher at the Fred Hutchinson Cancer Research Center here in Seattle, and friend of mine.  He's doing some very interesting research on nutrition and health (with an interest in ancestral diets), and I'm confident that we'll be getting some major insights from his research group in the near future.  Mario specializes in tightly controlled human feeding trials.  Ton is an agricultural scientist at the University of Kassel in Germany, who specializes in the effect of animal husbandry practices (e.g., grass vs. grain feeding) on the nutritional composition of dairy.  None of us have any connection to the dairy industry or any other conflicts of interest.

The paper is organized into three sections:

1. A comprehensive review of the observational studies that have examined the relationship between high-fat dairy and/or dairy fat consumption and obesity, metabolic health, diabetes, and cardiovascular disease.
2. A discussion of the possible mechanisms that could underlie the observational findings.
3. Differences between pasture-fed and conventional dairy, and the potential health implications of these differences.

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What Causes Type 2 Diabetes, and How Can it be Prevented?

In the comments of the last post, we've been discussing the relationship between body fatness and diabetes risk.  I think this is really worth understanding, because type 2 diabetes is one of the few lifestyle disorders where 1) the basic causes are fairly well understood, and 2) we have effective diet/lifestyle prevention strategies that have been clearly supported by multiple controlled trials.

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The 14-percent advantage of eating little and then a lot: Is it real?

When you look at the literature on overfeeding, you see a number over and over again – 14 percent. That is approximately the increase in energy expenditure you get when you overfeed people; that is, when you feed people more calories that they need to maintain their current weight.

This phenomenon is related to another interesting one: the nonlinear increase in body weight and fat mass following overfeeding after a period starvation, illustrated by the top graph below from an article by Kevin Hall (). The data for the squares on the top graph is from the Minnesota Starvation Experiment (). The graph at the bottom is based mostly on the results of a simulation, and doesn’t clearly reflect the phenomenon.

Due to the significant amount of weight lost in what is called above the semistarvation stage (SS), the controlled refeeding period (CR) actually involved significant overfeeding. Nevertheless, weight was not gained right away, due to a sharp increase in energy expenditure. That is illustrated by the U-curve shape of the weight gain in response to overfeeding. Initially the gain is minimal, increasing over time, and continuing through the ad libitum refeeding stage (ALR).

Interestingly, overfeeding leads to increased energy expenditure almost immediately after it starts happening. It seems that even one single unusually big meal will significantly increase energy expenditure. Also, the 14 percent is usually associated with meals with a balanced amount of macronutrients. That percentage seems to go down if the balance is significantly shifted toward dietary fat (), probably because the metabolic “cost” of converting dietary fat into body fat is low. In other words, large meals with a lot of fat in them tend to cause a reduced increase in energy expenditure – less than 14 percent. Shifting the balance to protein appears to have the opposite effect, increasing energy expenditure even more, probably because protein is the jack-of-all-trades among macronutrients ().

The calorie surplus used in experiments where the 14 percent increase in energy expenditure is observed is normally around 1,000 calories, but the percentage seems to hold steady when people are overfed to different degrees () (). Let us assume that one is overfed 1,000 calories. What happens? About 140 calories are “lost” due to overfeeding.

What does this have to do with eating little, and then a lot, in an alternate way? It allows for some reasonable speculation, based on a simple pattern: when you alternate between underfeeding and overfeeding, you reduce food consumption for short period of time (usually less than 24 h), and then eat big, because you are hungry.

It is reasonable to assume, based on the empirical evidence on what happens during overfeeding, that the body reacts to “eating big” as it would to overfeeding, increasing energy expenditure by a certain amount. That increase leads to a reduction in the caloric value of the meals during overfeeding; a reduction of about 14 percent of the overfed amount.

But the body does not seem to significantly decrease energy expenditure if one reduces food consumption for a short period of time, such as 24 h. So you have the potential here for some steady fat loss without a reduction in caloric intake. Keeping a calorie intake up above a certain point is more important than many people think, because a calorie intake that is too low may lead to nutrient deficiencies (). This is possibly one of the reasons why carrying a bit of extra weight is associated with increased longevity in relatively sedentary populations ().

Is this 14-percent effect real, or just another mirage? If yes, what does it possibly translate into in terms of fat loss? More on these issues is coming in the next post.

Interview with Aitor Calero of Directo al Paladar

Aitor Calero writes for the popular Spanish cooking and nutrition blog, Directo al Paladar ("straight to the palate").  We did a written interview a while back, and he agreed to let me post the English version on my blog.  The Spanish version is here and here.

Without further ado, here it is:

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The lowest-mortality BMI: What is the role of nutrient intake from food?

In a previous post (), I discussed the frequently reported lowest-mortality body mass index (BMI), which is about 26. The empirical results reviewed in that post suggest that fat-free mass plays an important role in that context. Keep in mind that this "BMI=26 phenomenon" is often reported in studies of populations from developed countries, which are likely to be relatively sedentary. This is important for the point made in this post.

A lowest-mortality BMI of 26 is somehow at odds with the fact that many healthy and/or long-living populations have much lower BMIs. You can clearly see this in the distribution of BMIs among males in Kitava and Sweden shown in the graph below, from a study by Lindeberg and colleagues (). This distribution is shifted in such a way that would suggest a much lower BMI of lowest-mortality among the Kitavans, assuming a U-curve shape similar to that observed in studies of populations from developed countries ().

Another relevant example comes from the China Study II (see, e.g., ), which is based on data from 8000 adults. The average BMI in the China Study II dataset, with data from the 1980s, is approximately 21; for an average weight that is about 116 lbs. That BMI is relatively uniform across Chinese counties, including those with the lowest mortality rates. No county has an average BMI that is 26; not even close. This also supports the idea that Chinese people were, at least during that period, relatively thin.

Now take a look at the graph below, also based on the China Study II dataset, from a previous post (), relating total daily calorie intake with longevity. I should note that the relationship between total daily calorie intake and longevity depicted in this graph is not really statistically significant. Still, the highest longevity seems to be in the second tercile of total daily calorie intake.

Again, the average weight in the dataset is about 116 lbs. A conservative estimate of the number of calories needed to maintain this weight without any physical activity would be about 1740. Add about 700 calories to that, for a reasonable and healthy level of physical activity, and you get 2440 calories needed daily for weight maintenance. That is right in the middle of the second tercile, the one with the highest longevity.

What does this have to do with the lowest-mortality BMI of 26 from studies of samples from developed countries? Populations in these countries are likely to be relatively sedentary, at least on average, in which case a low BMI will be associated with a low total calorie intake. And a low total calorie intake will lead to a low intake of nutrients needed by the body to fight disease.

And don’t think you can fix this problem by consuming lots of vitamin and mineral pills. When I refer here to a higher or lower nutrient intake, I am not talking only about micronutrients, but also about macronutrients (fatty and amino acids) in amounts that are needed by your body. Moreover, important micronutrients, such as fat-soluble vitamins, cannot be properly absorbed without certain macronutrients, such as fat.

Industrial nutrient isolation for supplementation use has not been a very successful long-term strategy for health optimization (). On the other hand, this type of supplementation has indeed been found to have had modest-to-significant success in short-term interventions aimed at correcting acute health problems caused by severe nutritional deficiencies ().

So the "BMI=26 phenomenon" may be a reflection not of a direct effect of high muscularity on health, but of an indirect effect mediated by a high intake of needed nutrients among sedentary folks. This may be so even though the lowest mortality is for the combination of that BMI with a relatively small waist (), which suggests some level of muscularity, but not necessarily serious bodybuilder-level muscularity. High muscularity, of the serious bodybuilder type, is not very common; at least not enough to significantly sway results based on the analysis of large samples.

The combination of a BMI=26 with a relatively small waist is indicative of more muscle and less body fat. Having more muscle and less body fat has an advantage that is rarely discussed. It allows for a higher total calorie intake, and thus a higher nutrient intake, without an unhealthy increase in body fat. Muscle mass increases one's caloric requirement for weight maintenance, more so than body fat. Body fat also increases that caloric requirement, but it also acts like an organ, secreting a number of hormones into the bloodstream, and becoming pro-inflammatory in an unhealthy way above a certain level.

Clearly having a low body fat percentage is associated with lower incidence of degenerative diseases, but it will likely lead to a lower intake of nutrients relative to one’s needs unless other factors are present, e.g., being fairly muscular or physically active. Chronic low nutrient intake tends to get people closer to the afterlife like nothing else ().

In this sense, having a BMI=26 and being relatively sedentary (without being skinny-fat) has an effect that is similar to that of having a BMI=21 and being fairly physically active. Both would lead to consumption of more calories for weight maintenance, and thus more nutrients, as long as nutritious foods are eaten.

Why Did Energy Expenditure Differ Between Diets in the Recent Study by Dr. Ludwig's Group?

As discussed in the previous post, a recent study by Dr. David Ludwig's group suggested that during weight maintenance following fat loss, eating a very low carbohydrate (VLC) diet led to a higher metabolic rate (energy expenditure) than eating a low-fat (LF) diet, with a low glycemic index (LGI) diet falling in between the two (1).  The VLC diet was 30 percent protein, while the other two were 20 percent.  It's important to note that these were three dietary patterns that differed in many ways, and contrary to claims that are being made in the popular media, the study was not designed to isolate the specific influence of protein, carbohydrate or fat on energy expenditure in this context. 

Not only did the VLC diet lead to a higher total energy expenditure than the LF and LGI diets, the most remarkable finding is that it led to a higher resting energy expenditure.  Basically, people on the VLC diet woke up in the morning burning more energy than people on the LGI diet, and people on the LGI diet woke up burning more than people on the LF diet.  The VLC dieters burned 326 more calories than the LF dieters, and 200 more than the LGI dieters.

It's always tempting to view each new study in isolation, without considering the numerous studies that came before it, but in this case it's essential to see this study through a skeptical lens that places it into the proper scientific context.  Previous studies have suggested that:

1. The carbohydrate:fat ratio of the diet has little or no detectable impact on energy expenditure in people who are not trying to lose weight (2, 3).
2. The carbohydrate:fat ratio of the diet has little or no detectable impact on energy expenditure in people who are being experimentally overfed, and if anything carbohydrate increases energy expenditure more than fat (4, 5).
3. The carbohydrate:fat ratio of the diet has little or no detectable impact on energy expenditure during weight loss (6, 7, 8), and does not influence the rate of fat loss when calories are precisely controlled. 

This new study does not erase or invalidate any of these previous findings.  It fills a knowledge gap about the effect of diet composition on energy expenditure specifically in people who have lost weight and are trying to maintain the reduced weight.

With that, let's see what could have accounted for the differences observed in Dr. Ludwig's study.
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New Study: Is a Calorie a Calorie?

A new study in JAMA led by Dr. Cara B. Ebbeling and colleagues purports to challenge the idea that all calories are equally fattening (1).  Let's have a look.  When thinking about the role of calorie intake in body fatness, there are basically three camps:

1.    Calories don’t matter at all, only diet composition matters.
2.    Calories are the only thing that matters, and diet composition is irrelevant.
3.    Calories matter, but diet composition may also play a role.

The first one is an odd position that is not very well populated.  The second one has a lot of adherents in the research world, and there’s enough evidence to make a good case for it.  It’s represented by the phrase ‘a calorie is a calorie’, i.e. all calories are equally fattening.  #1 and #2 are both extreme positions, and as such they get a lot of attention.  But the third group, although less vocal, may be closest to the truth. 
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