What is carb-loading?
Carb-loading involves either a reduction in glycogen for two days, or no change followed by a glycogen-loading period for four days where carbohydrate intake’s 70% of your diet. In both cases, the idea is that your cells are saturated with glycogen and so delay the onset of fatigue by up to 20%.
Does carb-loading affect men differently to women?
The majority of studies comprise of men, but as you highlight, there’s evidence that females might require a different race-fuelling strategy. These are based on gender-based metabolic differences that derive from different hormonal profiles, specifically the female hormone estradiol.
What is estradiol?
Estradiol’s secreted by the ovaries, peaking at ovulation. It’s been linked with numerous enzymes that play a role in metabolism, leading to enhanced triglyceride (a type of fat found in the blood) use in skeletal muscle. Concurrently, there’s no variation in glycogen levels during the menstrual cycle, suggesting female athletes are better fat-burners than men.
A study by Asker Jeukendrup measured fat-oxidation rates in 300 men and women over a range of exercise intensities and showed that women’s maximum fat oxidation (MPO) rate was 8.26mg of fat per kg of fat-free mass per min compared to 7.40mg in men. Their FatMax – the exercise intensity at which fat-burning peaks – was also higher, 52% of VO2max to the men’s 45%.
This efficient fat engine is one theory why the difference between male and female athletes shrinks the longer the event. One example is American Camille Herron, who smashed the overall 24hr and 100hr run records on the track.
How much should you carb-load?
In the 90s, professor Mark Tarnopolsky showed that, despite both genders increasing carb intake for four days from 55% to 75%, the women exhibited no muscle-glycogen increase and a 5% performance improvement. The men’s glycogen rose to 41% and performance by 45%. Tarnopolsky speculated that this was due to the women consuming less carbs per kg compared to men (6.4g/kg vs 8.2g).
So do women need more carbs pre-race?
Subsequent studies discovered that increasing carb intake to around 8g/kg helped. But, importantly, the overall energy intake, too. In fact, 30% more than normal. So a female triathlete might shift from 2,000cals a day with 60% from carbs to 2,600cals with 70% from carbs. That might compare with a man, who might shift from 2,500cals a day with 60% derived from carbs to 2,500cals a day with 70% from carbs.
So do women need to carboload as much as men before a race? The evidence suggests even more so, albeit ‘energy-load’s’ arguably a more appropriate term.