I’m a big proponent of training throughout the year and eating clean/staying lean during most of that time. Regardless, I know “indulging” will be inevitable so I wanted to offer my experience.
Junk Food really affects my workouts for several reasons.
1. With heavy/hard to digest foods I just get sleepy and don’t feel like being active. Fat has the biggest effect.
2. Most “cheat” foods are dehydrated. In fact, almost all of them, by definition. This will be the #1 thing that affects your performance and you cannot get enough water during the training session to compensate.
3. The dehydrating effect, as well as the thermogenic (heat-producing) effect of higher calories will elevate your body temperature. This is not a good thing as exercise elevates body temperature and you may heat up too much. At worst, you may have a heat stroke; at best, you’ll sweat buckets as your body cools itself.
4. A lot of cheat foods also contain several additives, mainly salt. No matter the source, salt is harmful to the body and it will be excreted through your sweat glands as the body works to re-establish proper mineral balance.
5. Cheat foods bloat you. Water retention makes you heavier; so does food in the gut. This is not a good feeling when trying to propel your body through space or get into challenging positions with a distended belly (try to pretend you’re not the “gaseous” person nearby)!
In short – you may be able to cheat and still look great; but I guarantee it will negatively affect your performance, physically and mentally.