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Why sugary drinks and protein-rich meals don't mix

Researchers say the combination causes the body to store more fat

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Eating meals that are high in protein is a great way to provide your body with the means to build and repair muscle, bones, and other important building blocks. However, a new study shows that pairing a sugary drink with a high-protein meal could be harmful.

Researchers from the USDA-Agricultural Research Service Grand Forks Human Nutrition Center have found that consuming sugar-sweetened drinks with high-protein foods negatively affects the body’s energy balance and can lead to it to store more fat.

"We found that about a third of the additional calories provided by the sugar-sweetened drinks were not expended, fat metabolism was reduced, and it took less energy to metabolize the meals. This decreased metabolic efficiency may 'prime' the body to store more fat," said lead author Dr. Shanon Casperson.

Reducing fat-burn

The study analyzed 27 healthy-weight adults over two 24-hour periods who were given protein-laden meals and sugar-sweetened beverages. Participants were given 15% protein meals on their first visit after an overnight fast and 30% protein meals under similar conditions on their second visit. On each visit, one sugar-sweetened beverage was consumed during one meal and one non-sugar-sweetened beverage was consumed during the other.

The researchers found that the sugar-sweetened drinks decreased the fat oxidation process after a meal by 8%, which means that it took longer for the body to start breaking down fat molecules. For the 15% protein meal, that translated to 7.2 grams of potential fat that wasn’t burned. For the 30% protein meal, that figure increased to 12.6 grams.

Additionally, Casperson says that the sugar-sweetened beverages changed participants’ food preferences, causing them to not feel satisfied with their meal and to crave different types of flavors and foods for long periods after eating.

"We were surprised by the impact that the sugar-sweetened drinks had on metabolism when they were paired with higher-protein meals. This combination also increased study subjects' desire to eat savory and salty foods for four hours after eating," she said.

Weight gain and obesity

The results of the study show that consumers who are looking to lose weight should avoid sugar-sweetened drinks, especially if they are consuming more protein to recover after working out.

"Our findings suggest that having a sugar-sweetened drink with a meal impacts both sides of the energy balance equation. On the intake side, the additional energy from the drink did not make people feel more sated. On the expenditure side, the additional calories were not expended and fat oxidation was reduced,” said Casperson. “The results provide further insight into the potential role of sugar-sweetened drinks -- the largest single source of sugar in the American diet -- in weight gain and obesity."

The full study has been published in BMC Nutrition.