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Supplementing a tough lifting workout with a protein shake is common practice at the gym. Based on the premise that weight training breaks down the muscle and protein helps build it back up, these popular products promise to maximize the muscle-building effects of a good workout.

Containing a mix of high-quality proteins, amino acids, electrolytes and carbohydrates, most protein supplements come in powder form and are mixed with water or milk. Sold at gyms, pharmacies, grocery stores, online and at specialized nutrition stores, the shakes appeal primarily to men who believe more protein equals more muscle. But a recent study published in Science and Sports noted that too much protein can build more fat than muscle.

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The researchers, who hail from France and Tunisia, hypothesized that when it comes to the use of protein supplements among gym enthusiasts, the gap between science and practice is huge. In other words, the average gym member is getting advice about supplements from peers at the gym, magazines and blogs versus more professional guidance that takes diet and gym habits into account. So while most studies in controlled conditions have shown protein supplements can be effective in building muscle, in real life their use is anything but controlled. Frequency of use, dosage and type of supplement fluctuate considerably from user to user, which has a significant impact on efficacy.