On-Demand Energy Without Getting Out of Ketosis?

I have lost all of my excess weight and most of my fat reserves following a ketogenic diet (3 mos.). I maintain a strict keto diet and log my daily macros religiously, limiting my carb intake to <20g/day. I exercise daily and am fit and healthy for a 64 year-old man. Last week I went on a moderately difficult hike after eating a breakfast of charcuterie at the hotel where I was staying. On the way back from the hike I ran out of energy. My leg strength failed and I began trembling. Eventually I had to be assisted down the mountain. I had raw pecans with me for food along the way but they did not provide my muscles the energy when I needed it.
What did I do wrong? Should I have eaten something like a high energy bar full of carbs? If I had, would that have taken me out of ketosis? This was an embarrassing and potentially dangerous situation that I don't want repeated.
Thank you for your advice!

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    While we can burn fat for energy during activity, it's not as efficient as using carbs. It sounds like the demand on your energy stores exceeded what your body could provide.

    In this situation, I absolutely think you needed to eat some carbohydrates to provide your body with immediate glucose that could be burned for energy. Typical recommendations for athletes are 30-60 g per hour for events lasting > 60-75 minutes. If you're not an athlete, you don't need to adhere to such strict guidelines, but I think something like a piece of fruit or some Gatorade would have been a great choice.

    I don't think that one banana would be enough to take you out of ketosis, but you do need to be careful not to eat too many carbs at one time as this can causes shifts in some of your nutrient levels, which can have a negative effect on the heart (short-term).

    Lastly, it's important to drink enough liquids, but avoid under and overconsuming water. Electrolytes are also important, especially if you are a heavy sweater.

    Kind regards,

    Susan Macfarlane, MScA, RD
    Registered Dietitian Nutritionist
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    Could you be low on magnesium?

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    Could be low sodium. It would cause muscle weakness.

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    Thank you all for your input. I closely monitor my vitamin and mineral requirements, so I know my magnesium and sodium levels are on OK. I think Susan is more on target in diagnosing my problem. In my zealeousness in following a keto diet I did not anticipate energy needs outside of my normal, daily routine. My body is very lean now and I do not have readily available fat stores to draw on for physically demanding activities. The nuts (fat) I ate on my hike did not provide the immediate energy I required at the time of my distress. In the future I will be better prepared. I hope others learn from my error.

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