Before we start off, some housekeeping:
This is the first post on a series I plan to make a part of FoodLabScience. I often encounter papers I find highly interesting, or containing information I think more people should know about. Therefore I am starting a new section in FoodLabScience called paper discussions. In this section I place more emphasis on single papers, to really extract and communicate the message I believe it contains. Let me know what you think!

Paper discussion #001 – The effect of sodas on our metabolism

By FoodLabScience

Evidence is mounting up for the proposition that one of the causes of the obesity crisis is a shift in macronutrient composition of the American diet.

What kind of shift has been seen? A report by the National Health and Nutrition Examination Survey from 1971-1974 on the energy percentages (%E) reported 44%E from carbohydrates, 17%E protein, and 37%E fat. In 2013-2014 it had changed to 49%E carbohydrates, 16%E protein, and 33%E fat. However the total energy intake had increases by 984 kJ per day, which translates to 235 kcal/day. Now why did the change in macronutrient composition lead to the increased energy intake? There are two expected mechanisms:

1. Multiple studies find evidence for an increase of daily energy consumption when the energetic consumption of protein is decreased. So there is a beneficial effect when more protein is consumed.
2. An increased consumption of what the authors call ‘sugar-sweetened beverages’ (SSBs). These SSBs are predominantly drunk as sodas alongside dinner. Consumption of SSBs with a meal, besides providing extra calories, causes a decrease in fat oxidation when compared to that meal with water. The SSB provides a detrimental effect, since fat oxidation is the amount of fat burnt by the body.

Now we get to the goal of this study, which is trying to see if the beneficial effect of increasing protein is offset by the inclusion of an SSB instead of a non-nutritive sweetened beverage (NNSB). A NNSB is like a soda, but artificially sweetened so that it contains no calories yet similar taste. They used the following approach.

They choose two meals, one standard (15%E protein), the other high in protein (30%E). Both meals contained the same total energetic content (500 kcal). They gave the meals to 27 healthy weight young adults (age = 23 ± 5). For each meal they gave the test-subjects either a SSB (120 kcal) or a NNSB (0 kcal). Afterwards they compared the effects on metabolism and desire to eat certain flavors.

Their first result is that the high protein meal lead to decreased hunger and increased satiety, as expected from results of other studies. It does seem that there is a correlation between protein consumption and a decrease in total energy intake. If an increase in protein consumption causes you to be less hungry, then it is likely you’ll also eat less in total.
Secondly, the high protein meal decreased the desire for savory, salty and fatty foods. This is an interesting result, since these flavor profiles are indicative of protein rich food (savory and salty) or fat rich food (fatty). It could be that, as the daily protein requirement of the body gets closer to being met, there is a change in the desired flavor profile that we crave in future food. This would be a regulatory way for the body to control which macronutrients are being ingested. The authors also note:

‘this study demonstrates, for the first time, that increasing dietary protein could potentially decrease fat intake from other food sources’.

Thirdly they found a decrease in diet-induced thermogenesis (DIT) for the case of an SSB. DIT, which is the energy the body expends to process the meal it just ingested, is part of the three ways our bodies consume energy (together with basal metabolic rate and physical activity). A decrease of 2.42% ± 5.91 was found. Highly variable, but a slight decrease nonetheless.
Finally a decrease in fat oxidation was found. Fat oxidation for the meal with SSB was on average 135 gram/day, while it was 145 gram/day for the meal with NNSB; on average a decrease of 10 gram fat per day. While 10 grams of fat per day might not seem much, this amounts to nearly 1 kilogram of extra weight (900 gram) after 3 months of drinking soda over water.

It is clear from these results that, while the quantitative effect does not seem very high, changing the macronutrient composition with the inclusion of soda and other sugary beverages can have an impact on population weight if the time is long enough. The subjects were young (age = 23 ± 5) and did not include overweight or obese people. More research will have to determine whether similar effects are found for these groups. Yet if you are struggling with weight issues, the results in this paper suggest increasing the protein content of your meals will help you lower feelings of hunger. Additionally it appears wise to not drink a soda with your meals, instead drink some water or something artificially sweetened if you still want the sweet taste.

This post was a discussion based on the following paper:
Casperson SL, Hall C, Roemmich JN. Postprandial energy metabolism and substrate oxidation in response to the inclusion of a sugar- or non-nutritive sweetened beverage with meals differing in protein content. BMC Nutr [Internet]. 2017;3(1):49.

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