Clocking into the gym: When is the best time to exercise for fat loss?

Opinions everywhere

A quick flick through your favourite fitness mags or wellness blogs reveals a myriad of different opinions about when the best time to exercise for weight loss is. Should you be doing fasted cardio first thing morning? Weight training in the evening? Or maybe high intensity interval training (HIIT) every hour on the hour? 

Let’s dispense with the ‘bro science’ and see what the current research actually suggests. 

In the morning

A 2016 meta-analysis sought to answer the question of whether or not exercise first thing in the morning increases the amount of fat burned. Results of this analysis clearly showed that the amount of fat burned for energy (known as beta oxidation) was higher in those exercising in the morning in a fasted state when compared to those that exercised at other times of the day.[¹] Furthermore, performing cardio first thing in the morning, while still in a fasted state, has also shown to increase blood flow to those pockets of stubborn fat (like love handles) that many of us want to be rid of. [²] This is important, as this increased blood flow leads to a greater mobilisation of fat from these areas.

Furthermore, performing cardio first thing in the morning, while still in a fasted state, has also shown to increase blood flow to those pockets of stubborn fat (like love handles) that many of us want to be rid of. [²]

In the evening 

On the other hand, completing your resistance (i.e. weight) training in the evening appears to enhance performance. According to a 2013 study, the maximum power output and time to exhaustion of the participant’s muscles were higher in the evening when compared to the morning.[³] While these findings have been called into question by other researchers,[⁴] the results do suggest you’ll be able to train harder for longer. This has benefits in terms of maximising muscle growth, which in turn leads to an increased metabolism and therefore, weight lost. 

Despite these benefits, it is important to consider the impact of an evening workout on your circadian rhythm. When looking at the science, a recent review concluded that vigorous exercise late in the evening may increase your nocturnal body temperature and activate the stress response (known as the sympathetic nervous system), which negatively impact sleep quality.[⁵] As a lack of quality sleep is strongly associated with weight gain[⁶] and a reduction in impulse control the next day, ensure the time of your workout isn’t impeding your ability to stick to your workout program in the first place. 

Weight loss is the overall goal

If you’re now not sure if you should be working out with the sunrise or sunset, never fear: the total amount of calories you burn across a day (known as your 24hr energy expenditure) is the same no matter when you exercise,[⁷] and it’s this marker is ultimately determines how much fat you’ll burn.[⁸] Therefore, the most important point is to do some regular exercise. While anything is better than nothing, a minimum of 3 hours of moderate intensity cardio, or 100 minutes of high-intensity interval training (HIIT) weekly, is required to facilitate changes in body composition.

Whilst anything is better than nothing, a minimum of 3 hours of moderate intensity cardio, or 100 minutes of high intensity interval training (HIIT) weekly, is required to facilitate changes in body composition.

 Further, the more regular the timing of that exercise, the easier it is for the body to adapt to the routine and facilitate proper recovery. This is important, as those who can develop a consistent routine are more likely to stick to their exercise goals than those who engage in exercise ad lib.[⁹]

The verdict 

Overall, the current research shows us that a regular exercise routine, regardless of when you complete it throughout the day, is beneficial in helping you to reach your weight loss goals. However, exercising fasted in the morning may provide additional benefits in terms of shifting stubborn fat stores, and looks to be the better option if you’re needing to regulate or maintain a healthy sleep cycle. On the other hand, an evening resistance workout may help you to build more muscle, but could upset your circadian rhythm if it is performed too late at night. 

Therefore, taking into consideration the health of your sleep cycle plus your goals for working out, will allow you to build an exercise regime that’ll provide you with the best outcomes.

1] Vieira AF, Costa RR, Macedo RC, Coconcelli L, Kruel LF. Effects of aerobic exercise performed in fasted v. fed state on fat and carbohydrate metabolism in adults: a systematic review and meta-analysis. Br. J. Nutr. 2016 Oct;116(7):1153-64. DOI: 10.1017/S0007114516003160.

[2] Gjedsted J, Gormsen LC, Nielsen S, Schmitz O, Djurhuus CB, Keiding S, et al. Effects of a 3‐day fast on regional lipid and glucose metabolism in human skeletal muscle and adipose tissue. Acta physiol (Oxf). 2007 Nov;191(3):205-16. DOI: 10.1111/j.1748-1716.2007.01740.x.

[3] Edwards BJ, Pullinger SA, Kerry JW, Robinson WR, Reilly TP, Robertson CM, et al. Does raising morning rectal temperature to evening levels offset the diurnal variation in muscle force production?. Chronobiol. int. 2013 May 1;30(4):486-501. DOI: 10.3109/07420528.2012.741174.

[4] Seo DY, Lee S, Kim N, Ko KS, Rhee BD, Park BJ, Han J. Morning and evening exercise. Integr Med. res. 2013 Dec 1;2(4):139-44. DOI: 10.10.16/j.imr.2013.10.003.

[5] Uchida S, Shioda K, Morita Y, Kubota C, Ganeko M, Takeda N. Exercise effects on sleep physiology. Front neurol. 2012 Apr 2;3:48. DOI: 10.3389/fneur.2012.00048

.[6] Atkinson G, Davenne D. Relationships between sleep, physical activity and human health. Physiology & behaviour. 2007 Feb 28;90(2-3):229-35. DOI: 10.1016/j.physbeh.2006.09.015

.[7] Schoenfeld BJ, Aragon AA, Wilborn CD, Krieger JW, Sonmez GT. Body composition changes associated with fasted versus non-fasted aerobic exercise. J Int. Soc Sports Nutr. 2014 Dec;11(1):54. DOI: 10.1186/s12970-014-0054-7.

[8] Schoenfeld B. Does cardio after an overnight fast maximize fat loss?. J. Strength Cond res. 2011 Feb 1;33(1):23-5. DOI:10.1519/SSC.0b013e318.

[9] Alley JR, Mazzochi JW, Smith CJ, Morris DM, Collier SR. Effects of resistance exercise timing on sleep architecture and nocturnal blood pressure. J. Strength Cond res.  2015 May 1;29(5):1378-85. DOI: 10.1519/JSC.0000000000000750. 

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