Full Disclosure: ‘I have partnered with CurraNZ (www.curranz.co.nz), the blackcurrant health & fitness supplement company to do a series of blog posts on the science behind the benefits of NZ blackcurrants. This content is sponsored to the extent that CurraNZ has paid for my time to review the research, the copy/opinions here are my own.’
Our metabolic and physiological health depends on our ability to oxidise fuel for energy, and while we use amino acids and lactate as fuel under specific conditions, this predominantly refers to the use of carbohydrate or fat. Humans are born metabolically flexible and easily able to burn both fat and carbohydrate as fuel. In an ideal situation, people readily burn fat as fuel at low intensities (of which most people have an unlimited supply) and save the limited stores of carbohydrate to be used as exercise intensity ramps up.
The fuel used when training and competing is influenced both by training status (the fitter the athlete, the easier it is to use fat as a fuel source) and our food environment (i.e., the food eaten). In the modern food environment particularly, we can see a preference towards burning carbohydrate over fat even at rest due to the higher carbohydrate load of the diet. As carbohydrate is a limited fuel source, and metabolising it creates more oxidative stress, free radical production, and inflammation, this isn’t an ideal scenario for both metabolic health or training and sports performance. The enzymes that are required to oxidise fat can be downregulated over time, reducing the ability to use fat as a fuel source and spare glycogen (stored carbohydrate). As athletes we want to be able to use both fat and carbohydrate, to help fuel over short and long-distance events, and minimise excess free radical production, thus not only improve performance, but reduce inflammation and recovery time.
Blackcurrant extract has been studied for its potential to enhance fat oxidation in the performance setting in both trained females and males. An average improvement in ability to burn fat by over 25% has been found in endurance-trained females in a 2h steady state cycling test (at 65% VO2 max) when they took the New Zealand blackcurrant supplement over a 7 day period. This is notable given that the ceiling at which improvements can be made in a trained individual (with already good fat-oxidation abilities) is generally smaller than that of an untrained individual. Variable doses were trialled, and 2 capsules (equivalent to 600mg extract) per day was found to provide the best cost-benefit ratio.
Further, men and women who took 600mg of the blackcurrant supplement each day for 7 days increased their fat burning capacity by an average of 30% in 60 minutes of steady state running at temperatures of 34 degrees Celsius compared to a placebo condition. This suggests that the supplement may spare glycogen to some extent, which is often burned at a higher rate in more ambient temperatures. While this was not found to be the case in hypoxic conditions (the environment overrode the effect of the supplement), when taken in conjunction with a standard carbohydrate gel over a 120 min treadmill test, the supplement was able to increase fat oxidation by close to 25% and spare glycogen use by 11% in a case study analysis. While more research is warranted, these are encouraging results for any athlete looking for a competitive edge.