Supplement analysis backed by scientific evidence · PT

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Moderate evidencePhysical performance

Glycerol

Glycerol reliably increases fluid retention and expands body water before exercise, which is a real physiological effect. Whether that translates into faster times is much less certain: the performance benefit shows up mainly in hot conditions where dehydration would otherwise be substantial.

What the science says

  • Hyperhydration and fluid retention Moderate evidence

    Glycerol added to a sodium-containing hyperhydration drink retains more fluid than salt alone or glycerol alone, with retained volumes typically several hundred millilitres greater than water in controlled crossover trials. The osmotic mechanism is well characterised and reproducible.

  • Endurance performance in the heat Limited evidence

    A 2023 systematic review of pre-exercise hyperhydration found performance benefits were inconsistent and concentrated in protocols where participants would otherwise have become significantly dehydrated. Well-controlled trials, including a half-marathon time trial in warm conditions, found glycerol plus sodium produced no performance advantage over sodium alone.

  • Thermoregulatory strain Moderate evidence

    Hyperhydration lowers core temperature and heart rate during exercise in the heat in most trials, a plausible mechanism for benefit in long hot events even where finishing times do not change. The magnitude is small, on the order of 0.1-0.3 degrees C.

  • Added body mass offsets the benefit Moderate evidence

    Retaining 1-1.5 L of extra fluid adds 1-1.5 kg to carry. In weight-bearing events, especially uphill running, this can cancel the thermoregulatory gain, which is one reason results are inconsistent.

Dosage & safety

Studied dose1.0-1.4 g/kg body mass of glycerol dissolved in 25-30 mL/kg of fluid, consumed over 30-60 minutes and finishing 60-120 minutes before exercise. Adding sodium (roughly 3 g/L) improves retention beyond glycerol alone. Practise it in training first, as GI tolerance varies a lot.
SafetyCommon side effects are nausea, bloating, headache and light-headedness, mostly from the large fluid volume. The added 1-1.5 kg of body water is undesirable in weight-sensitive sports. Avoid in kidney disease or heart failure. Regulatory note: glycerol was on the WADA Prohibited List as a plasma expander and potential masking agent until it was removed in January 2018, so it is now permitted, but competitive athletes should confirm current national anti-doping guidance. Use medical input if you have diabetes, as glycerol is a gluconeogenic substrate.

Scientific references

Where to buy

GAINS, Instantized Glycerol, Soluble Glycerol Powder, 14.11 oz (400 g)

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