Health- and fitness-related New Year's resolutions are some of the most common promises people make to themselves at the end of the year, striving to undo the damage done by overindulging over the holidays. Unfortunately, these pledges tend to have high failure rates, largely due to unrealistic expectations. For those finding it difficult to stick to a New Year's resolution, don't give up. Look at health and fitness from a more realistic perspective, and understand that quick fixes are just that - they're not meant to be sustained long term.
● Crash diets aren't sustainable
Crash diets produce such impressive results initially due to the effects of starvation on the body, most notably that insulin levels decrease and encourage the kidneys to release sodium, tackling common symptoms of bloating. However, this effect only lasts until the body regulates its mineral balance, and weight loss begins to slow, affecting motivation to continue with the diet.
Research suggests that crash diets produce less significant effects in the long term when compared to traditional diets due to the nutritionally unbalanced nature of severely restricted eating habits. Reports indicate that, on average, crash dieters weigh approximately one pound more than their starting weight  12 months after beginning a very low calorie diet.
The NHS recommends that those looking to shed the pounds and become healthier strive to lose weight at a steadier, more sustainable pace of between one and two pounds per week. Dieters are advised to restrict caloric intake by roughly 500 to 600 calories less than the recommended amount based on gender, and to incorporate exercise into the daily routine.
● Intense workouts are hard to maintain
Fitness-related New Year's resolutions can encourage significant changes in health and wellbeing, but too much too soon could prove to be detrimental. For those unaccustomed to physical activity, sudden intense workouts can increase the risk of cardiovascular events and may be difficult to sustain long term due to injury or fatigue. Always consult your GP if you are intent on starting a new intensive fitness regime but are unaccustomed to exercising on a regular basis.
Research suggests that lower intensity workouts are much easier to maintain in the long term, ultimately producing more beneficial results. In terms of weight lifting, for example, a 10 percent reduction in load can significantly improve sustainability, while greater rest periods of 240 seconds during resistance training  can boost the number of repetitions undertaken.
The NHS recommends that healthy adults wanting to improve fitness should partake in 150 minutes of moderate intensity exercise each week. Moderate intensity exercises include walking, cycling, water aerobics, gardening, or playing sports such as tennis, volleyball, or basketball. The exercise should increase heart rate and quicken breathing, but not induce sickness.References:
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Special Issue: Dietary Patterns for Weight Management and Health. Volume 9, Issue S11, pages 295S-301S, November 2001
 Apfelbaum, M et al. "Long-term maintenance of weight loss after a very-low-calorie diet: a randomized blinded trial of the efficacy and tolerability of sibutramine". The American Journal of Medicine
Volume 106, Issue 2, February 1999, Pages 179-184
 Danilo Calori et al. "Acute effect of different weight exercise intensities in muscular performance of trained older women". Rev Bras Med Esporte vol.18 no.6 São Paulo Nov./Dec. 2012
 Bahman Mirzaei et al. "Comparison of 3 different rest intervals on sustainability of squat repetitions with heavy vs light loads". Brazilian Journal of Biomotricity