But wouldn’t it affect my training for the 21k, and I have a 8k in 3 weeks?
I know I need to rest but, feel like it will delay my training…
I’m not sure. Continuing to push yourself too hard could have a negative impact on your marathons. If you continue without giving your body rest, then you might burn out completely. You might not even be able to participate at all from the exhaustion. Your body will simply break down and become sick—or even worse injured.
Taking a week off shouldn’t negatively impact your training. If you’re not ready for the marathon fitness-wise, then perhaps it’s not the best idea to go for it this soon. On the other hand, taking a week off could actually be beneficial and reap tons of benefits. It will give your body the much-needed rest that it’s clearly begging for. You could come out of your break more energized and stronger than before. Thus you’d be able to physically push yourself further than you can in your present state.
It’s just like after a very vigorous weight training session. You wouldn’t train the same muscles two days in a row after going all out the day before. No. You need to give them enough rest (AND NUTRITION!) in order to repair the damage that physical activity does, and to grow. The strength comes after the regrowth and repair of the muscle.
I didn’t get an adverse impression from you about nutrition, but hopefully you’re fueling yourself properly. Increased activity naturally leads to an increase in hunger. And there’s nothing wrong with fueling your body when you’re actually hungry because your body needs it. Depriving yourself of nutrition when your body needs it will lead to slowed muscle repair. Which could further contribute to burning out, poor performance, and injury. Although it’s better to give your body healthy fats and protein vs unhealthy carbs and processed “cravings”.
Anyway, this is merely my opinion and my suggestions to you. I hope you’re able to overcome your dilemma! I’ve felt like you feel right now, and it sucks. It forced me to change my habits, and even take periodic longer breaks than simply a day or so a week, because I knew I couldn’t keep it up. Maybe a week of absolutely nothing fitness-related is exactly the break you need. Not only for your body, but for your mind as well? All of this training and focus on fitness is taxing both physically and mentally.