Strict adherence and extreme discipline with exercise and nutrition are something I think our culture mistakenly commends. The act of going on or being on a diet is still a widespread method of attempting weight control. Luckily, new trends point toward "a healthy lifestyle", allowing for some slips and trips along the way.
One of the first things I try to get clients to acknowledge is that in nutrition there are no “absolutes” when it comes to a healthy lifestyle (although there are a few exceptions, for example, absolutely no smoking to prevent heart disease and lung cancer). There are no absolutes because not one piece of advice is absolutely applicable to everyone, 100% of the time. I have seen too many times that an all-or-nothing approach to fitness and nutrition leads people down an unfortunate path into a vicious cycle of "re-starts".
Your health is intermingled with an infinite number of factors in your lifestyle. There are a million things that affect your food choices in your own mind and body, let alone among your surroundings. Therefore, if you have resolved to eat healthier all the time, and to never have treats, you will be faced with a myriad of temptations that threaten your reaching of your goals. This all-or-nothing kind of approach to nutrition and exercise, no matter how short or long term it is planned for, will MOST likely NOT produce sustainable results. Your approach to nutrition and fitness must be moldable and transformable; in this, it will be transformative.
The real discipline I encourage my clients to possess is patience. Long-term success requires patience with your body’s natural tendency to want to preserve and store energy for use in times of famine and in order to survive. Whether you have a goal of 100 pounds to lose or 10 miles to run, you have the ability to push your body and mind beyond the “survival” mechanism into a state of “thriving”. Reassure the physiological reflexes with some moderate and incremental increases to your current fitness routine, and with high-nutrient, fibrous foods that fill you up and nourish you on a cellular level.