Study suggests that, for optimal fat loss, the best thing to eat before exercise is nothing at all

The night before someone runs a marathon, there’s a fair chance they’ll chow down on pasta. The carbohydrate in pasta is supposed to help stock the liver and muscles with glycogen (a form of starch) which can then be used to fuel one’s efforts the following day. Such an approach is said to reduce the risk of glycogen depletion which can lead to a serious downturn in output colloquially referred to as ‘hitting the wall’.

The concept of endurance athletes stocking up on carbs has, I think, fuelled the notion that we should ideally have some sort of fuel inside of us prior to exercise. However, as I explain here, there is an argument for avoiding spikes in blood sugar is seeking to maximise one’s capacity to utilise fat as a fuel during exercise. I think there’s an argument for consuming little or nothing before exercise unless, perhaps, exercise is to be very prolonged.

I was interested to read about a recent study in which the effect of feeding prior to exercise on fat burning was tested [1]. In this study, a group of overweight men were assessed in the morning in each of three conditions:

  1. A set breakfast with no exercise
  2. A set breakfast followed by 60 minutes of exercise at 50 per cent maximal intensity
  3. A set breakfast following 60 minutes of exercise at 50 per cent maximal intensity

Three and a half hours later the men were given lunch which they could eat in unlimited quantity. Intakes at this lunch were essentially the same on all three occasions.

The study subjects were also assessed in terms ‘fat balance’ (the relative amounts of fat consumed and metabolised) over an 8.5-hour period. Overall, fat balance was favourable after exercise compared to no exercise. However, the effects were significantly more favourable if breakfast was taken after exercise, rather than before.

The ‘fat deficit’ equated to 250 calories if breakfast was taken after exercise, compared to 167 calories if breakfast was taken before.

This is just one study, done in a limited number of people, with each condition tested only once and in quite a controlled fashion, so let’s not over-interpret the results. However, there is evidence here which supports the notion that, for the most efficient fat-burning, exercise may perhaps be best performed on an empty stomach.

References:

1. Farah NMF, et al. Effects of exercise before or after meal ingestion on fat balance and postprandial metabolism in overweight men. British Journal of Nutrition. Published online: 26 October 2012

8 Responses to Study suggests that, for optimal fat loss, the best thing to eat before exercise is nothing at all

  1. Chloe Brotheridge 13 November 2012 at 3:18 pm #

    It makes perfect sense that if your musles are depleted of glycogen after having fasted all night, that your fat reserves are more likely to be called upon for fuel. However most mainstream health professionals insist that the time of day that you consume the calories is not important, only the number of calories in a day. I noticed a story in the Telegraph yesterday http://www.telegraph.co.uk/health/healthnews/9671177/Eating-late-at-night-makes-you-fat.html about how eating late at night can cause weight gain. It’s far too simplistic to think that our weight is controlled simply by calories in and calories out, no matter when they’re eaten or from what source.

  2. James 13 November 2012 at 11:14 pm #

    Hello there,

    I just saw your low carb expert cruise talk on youtube. Not only informative very hilarious! Now on topic: I have been on low carb / high fat / moderate proteins for 6 weeks now and am fully keto-adapted by now. I can confirm your statements in this article: I feel much better exercising after a period of fasting. I have experimented a little lately and whether I fast for 8 – 16 or even 24 hours (because I truly don’t feel hungry at all), I can exercise without any problems. But when I feel hungry, I eat until I am completely full :) This new lifestyle is one of the greatest things that I experienced and I will simply stick to it.

  3. Helen Howes 14 November 2012 at 12:55 pm #

    I read the study.. The breakfast was horrific.. High carb and artificial, almost no fat..

  4. Joy 16 November 2012 at 2:03 pm #

    What about those who have problems with adrenal function such as CFS/ME?

    If the adrenals are underperfoming would we want to add the stressor of exercising with no fuel?

  5. Jonathan Bagley 17 November 2012 at 2:28 am #

    A few years ago I read something about professional Rugby Union players training on an empty stomach. Could have been Gabby Logan talking about her husband, Kenny.

  6. Dr. Bill Wilson 17 November 2012 at 8:10 am #

    There is emerging evidence that the best way to lose fat is to eat a low carbohydrate, moderate protein, HIGH fat diet combined with intermittent fasting. Yes indeed, this is almost the exact opposite of what the medical profession has been telling us to do for decades. Eating a high fat diet–assuming they are healthy fats, seems to help our bodies get used to using fat for energy rather than glucose from carbohydrates. The extreme form of this type of diet is a ketogenic diet. The popular low carb blogger Jimmy Moore is into this type of diet.

    If you are “fat adapted”, skipping breakfast allows you to burn your own fat for energy rather than using your own lean body mass to produce glucose through the process of gluconeogenesis.

    Most people with adrenal problems actually have a brain condition called CARB syndrome. The brain actually controls the endocrine organs and when your brain isn’t functioning as intended, your adrenal glands, along with your thyroid gland and sex organs will also be out to lunch.

  7. Sue G 18 November 2012 at 7:27 pm #

    Interesting. I have found that whilst I can walk the dog before breakfast and thus no food without any ill effects, if I walk him in the afternoon, fairly late, say 16.00, then I often get a feeling in my stomach that almost makes me want to rip it out, I feel dizzy and quite off. Eating as soon as I get in alleviates this.

    Hypoglycaemic perhaps? I don’t know. I wouldn’t want to try anything taxing though, I suspect I may fall over.

  8. Dr. Bill Wilson 23 November 2012 at 12:59 am #

    Sue G–Yes it is likely hypoglycemia due to being “carb adapted” with a dollop of insulin resistance. Substitute heathy fats for carbs and over time this reaction should slowly go away.

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