Hi Martin
As previously mentioned, the most important thing is your overall diet rather than focusing on snacks before and after a workout. The process of building muscles is a long one – during exercise, the muscles get damaged, and the body then needs to repair and re-build them to form even stronger, greater muscle mass under the correct nutritional and recovery conditions.
Therefore, you should seek the help of a qualified personal trainer to ensure your muscles are trained correctly with appropriate recovery period to enable muscle growth.
From the nutritional point of view, your diet should be high in protein like eggs, fish, meat, pulses, nuts and seeds and abundant in vegetables that supply antioxidants that help you to repair and build muscles (aim for 8 portions a day). Excellent sources of antioxidants (including vitamin C) in fruit are berries and tropical fruit like oranges and mandarins.
Whole grain products (whole grain bread, brown rice, quinoa, pulses) are essential for slow-release energy so you can train for longer
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Healthy fats are also vital and should be included in your diet. A nutritional therapist can help you establish the correct ratio of nutrients in your diet based on your needs.
Therefore, to answer your question and to add to the list, good pre-workout snacks could be whole grain bread/pancakes with jam, banana with roasted nuts and maple syrup, strawberries with whipped cream and post-workout snacks could be oatcakes with guacamole or boiled egg, dark chocolate (70% or higher), and vegetable sticks with hummus.
However, if you find it difficult to build muscle mass following an adequate diet, you might need to seek an advice of your doctor. Excessive production of the hormone cortisol (the stress hormone) by your body can cause muscle breakdown and wasting hence it needs to be corrected before you can see results.
Good luck!