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    EXPERT INSIGHTS: Why increasing fat burning by 25% is notable, particularly for trained athletes

    on August 14, 2023

    Mikki Williden is a registered nutritionist and PhD who has advised thousands of people on achieving their health and performance goals through nutrition, with a hugely successful weight loss program called Mondays Matter. 

    Also an ultra-endurance athlete, Mikki is a co-host of Fitter Radio and has a popular podcast, Mikkipedia, where she dives into all matters relating to health, fitness and longevity.  

    Here, Mikki runs the rule over the CurraNZ fat oxidation research, which now numbers 14 studies and explains its place for performance and health.


    'The impacts of metabolising carbohydrate aren't ideal for metabolic health, training or sports performance'

    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, writes Mikki Williden.

    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 oxidised fat can be down-regulated 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 [CurraNZ] 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 (1) in a two-hour steady state cycling test (at 65% VO2 max) after seven days intake of the New Zealand blackcurrant supplement.

    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 (2), and 2 capsules (equivalent to 600mg extract) per day was found to provide the best cost-benefit ratio.

    Blackcurrant extract increased fat burning in runners by 30% in hot conditions, but not at altitude

    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 (3).

    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)(4), 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 (5).

    While more research is warranted, these are encouraging results for any athlete looking for a competitive edge.


    1. New Zealand blackcurrant extract enhances fat oxidation during prolonged cycling in endurance-trained females. Strauss, JA, Willems, MET and Shepherd, SO (2018) European Journal of Applied Physiology. ISSN 1439-6327
    2. Dose Effects of New Zealand Blackcurrant on Substrate Oxidation and Physiological Responses During Prolonged Cycling, Matthew David Cook,  Mark Willems, Eur J Appl Physiol (April 2017) 117:1207–1216DOI 10.1007/s00421-017-3607-z
    3. Dietary supplementation with New Zealand blackcurrant extract enhances fat oxidation during submaximal exercise in the heat, Mark E.T. Willems, Journal of Science and Medicine in Sports, March 2020 DOI: 10.1016/j.jsams.2020.02.017
    4. Effect of New Zealand Blackcurrant Extract on Cycling Performance and Substrate Oxidation in Normobaric Hypoxia in Trained Cyclists. Mark Willems 1,* , Mehmet Akif ¸ Sahin, and Matthew David Cook. Sports 2019, 7(3), 67;
    5. Running-induced metabolic and physiological responses by New Zealand blackcurrant extract in a male ultra-endurance runner: A case study J. Funct. Morphol. Kinesiol. 2022, 7, 104.