Sunday, November 27, 2016

DIT: Four Fat-Burning Facts About the Effects of Calories, Macros + Meal Timing on the Thermogenic Effects of Foods

A dream has come true: You can burn more calories by eating more... unfortunately, the so-called "diet-induced thermogenesis" does not fully compensate the increased energy intake - you cannot eat yourself slim as "unfair" as some people think this was.
You all will have read that: eating a high protein meal first thing in the AM kickstarts your metabolic engine. But do you also know that this "kick" is worth - in terms of calories, for example? Do you know how the mix of carbohydrates, fats and proteins will affect your diet-induced thermogenesis? Can you tell if calories matter and whether the meal size and speed at which you consume a given meal will matter?

Well, today's SuppVersity article will not be able to answer all of these questions in a "once and for all" fashion, but being based on the latest systematic review by Quatela et al. (2016), it will still give you a good overview of the individual effects of differing energy intakes, macronutrient compositions, and eating patterns of meals on what scientists call your DIT, i.e. your "diet-induced thermogenesis" (DIT) in response to a std. meal.
While fasting will obviously not trigger DIT, it relates to the effects of meal frequency on DIT

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The previously hinted at review comprised 26 papers - all with a randomized crossover design capable of comparing the effects of two or more eating events on DIT. And here's what the authors found:

Higher energy intake increased DIT; in a mixed model meta-regression, for every 100 kJ increase in energy intake, DIT increased by 1.1 kJ/h (p < 0.001 | Quatela. 2016). 

There's, for example, the 1990 study by Kinabo and Durnin who found no effect of the macronutrient composition of the test meals they served either high-carbohydrate-low-fat (HCLF) with 70%, 19% and 11% of the energy content from carbohydrate, fat and protein, respectively, or a low-carbohydrate-high–fat (LCHF) with 24%, 65% and 11% to sixteen adult, non–obese female subjects.
Figure 1: Studies like Kinabo & Durnin (1999) show that low carb vs. low fat does not make a difference - what does matter for DIT (and that's statistically and practically sign.) is the total energy intake per meal.
Accordingly, the two scientists concluded that "[t]he present study suggests that TEF is significantly influenced by the energy content of a meal but not by meal composition" (Kinabo. 1990) - very similar observations, albeit not always with meals differing in their macronutrient composition, have been made by Hill et al. (1984), and Segal et al. (1990).
There's a 50% difference in the thermogenic response to a std. meal (720kcal; the other meal was 35% of the RMR and thus not identical for both groups) in lean vs. obese men - in fact, the obese don't show any stat. sign. DIT (Segal. 1990).
Beware of becoming obese - It will impair your DIT: Even if the last-mentioned study by Segal et al. (1990) confirms that higher energy intakes will yield higher degrees of post-prandial diet-induced thermogenesis (DIT), it is far more important that this study is the first in a recently expanding line of studies that shows that this effect of high-energy meals is blunted in the obese (see Figure on the left). And there's more: With a 9-10% increase in thermogenesis in lean men, the 5% increase in the obese subjects is small and statistically and practically non-significant enough to count as one of the many reasons why obese individuals cannot get away with occasional binges as easily as those who are still lean.
With 100 kcal extra producing on average a thermogenic effect of only 1 kcal/h you got to be careful, though. Eating more is not going to burn body fat! What the research does suggest, however, is a possible explanation for the efficacy of intermittent fasting, where you can consume at least one really satiating, highly thermogenic high energy meal per day.

Meals with a high protein or carbohydrate content had a higher DIT than high fat, although this effect was not always significant (Quatela. 2016). 

The next take home message takes us back to my claim from the introduction: you all will have heard about the beneficial metabolic effects of high protein breakfasts. And in contrast to what the take home message says about carbohydrates, the evidence that high(er) protein intakes yield higher levels of diet-induced thermogenesis has been found consistently (see green lines in the Table 1) .

Table 1: Colored version of an overview from the review by Quatela, et al. (2016) - yellow = study shows advantage for CHOs; gray = study didn't find effect of high carb vs. high fat; green = study shows advantage for protein.
The effects of eating high carb and low carbohydrate meals on thermogenesis, on the other hand, is less clear. While there are studies showing that "low carb = more DIT" (see yellow lines in Table 1), there are also studies which observed identical effects for both, high fat and high carb meals (see gray lines in Table 1). a certain amount / percentage of protein, that's what the data in Table 1 tells us, is not enough for an optimal DIT to occur.

What should also be mentioned, though, is the fact that there's ZERO evidence to the opposite, i.e. an acute increase in thermogenesis to high fat intakes, when the meal size / energy content is standardized and the protein content is kept the same... and no, the study by Riggs et al. (2007) is not an example that this statement was wrong. After all, the "high fat" group in Riggs' study also received increased amounts of protein. The effects on DIT the scientists observed may thus well be ascribed to the extra 10% protein, not to the increased fat and/or reduced carb content.
You better don't starve yourself either! While the previous red box has thought you about the ill consequences being obese will have on your body's ability to burn off extra calories, the previously mentioned study by Riggs et al. shows that being too thin, i.e. underweight (starved), appears to have the same effect. In their study a higher protein intake lead to an increase in DIT only in the normal- yet not in the under- and overweight women; and that the exact same lack of thermogenesis can be observed in weight-reduced formerly obese subjects has been observed by Schutz et al. (1894) more than 40 years ago.
Simply distinguishing between calories and macros, alone, however, is not sufficient to predict the real-world DIT effect of a given meal. This (hopefully) unsurprising revelation takes us right to the last two take home messages that relate to the DIT effect of certain micronutrients and the importance of meal frequency.

Meals with medium chain triglycerides, and meals high in PUFA had a significantly higher DIT than other fats (meta-analysis, p = 0.002 | Quatela. 2016). 

Yes, it is true MCT oils are not just rapidly metabolized, there's also good evidence that they can increase the diet-induced thermogenesis in mouse and, more importantly, man (Kasai. 2002a,b; Clegg. 2013 | discussed => here).
Figure 2: The thermogenic effect of a meal does also depend on the type of fat in it (Casas-Agustench. 2009)
In a similar vein, the likewise comparatively easily oxidized PUFAs have been found to increase DIT compared to both MUFAs, i.e. monounsaturated, and - even more so - SFA, i.e. saturated fats (Piers. 2002; Casas-Agustench. 2009)

Consuming a meal as a single bolus eating event compared to multiple small meals or snacks was associated with a significantly higher DIT (meta-analysis, p = 0.02 | Quatela. 2016).

The last of our four take home messages is one you have read in previous SuppVersity articles about the advantages and disadvantages of fasting and/or a lower meal frequency, before. If you compare the effects of consuming a standardized meal as a bolus event versus splitting the same meal into two (Kinabo. 1990), three (Vaz. 1995), four (Allirot. 2013) or six (Tai. 1991) smaller equal meals or snacks to be consumed throughout the morning, the bolus administration will always produce the highest thermogenic response.
Figure 3: Mean differences in DIT between bolus vs. frequent smaller meals (e.g. snacking | Quatela. 2016)
This effect, however, is not significant in the two small meals and three small meals conditions. And still, Quatela's meta-analysis of all four studies (see Figure 3) shows that "[t]he overall mean of the difference is positive, which means that the DIT was lower in the smaller frequent meals event trials compared to the bolus trial" (Quatela. 2016).
The degree of processing will likewise affect the thermogenic response to food (Barr. 2010).
And there's still more: Unprocessed foods are more thermogenic than processed foods (Barr. 2010). The same goes for eating fast vs. slow (slow increases DIT compared to fast eating). It should be mentioned though that at least for the latter variable, as well as the effect of and palatability the evidence is either insufficient, unclear or contradictory. That's why I would agree that only "the energy intake, macronutrient compo-sition, and eating pattern of the meal" (Quatela. 106) have a sufficiently proven practically relevant effect on DIT.

With that being said, I cannot let you go without reminding you that neither the extra 10kcal/h you expend if you add another 1000kcal to your meal nor 17% increase in DIT you can get from increasing a meal's protein content will strip an inch off your waist or decrease your body fat percentage by 0.1% - and comprehensive evidence on the long-term effects is still warranted (for meal frequency there's some; the same goes for high protein). Optimizing your DIT should thus be only one (and not the most important) strategy in your dieting toolbox  | Comment.
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