Along with all its demonstrated and potential benefits, calorie restriction may result in a range of negative side effects.Those interested in the calorie-restricted lifestyle should be aware of the following potential issues:

• "negative" appearance changes -- CR-induced weight loss can affect the appearance ofthose who pursue it. In the overweight, these changes may be perceived positively -- but in others, negative perceptions may arise.
• bone health -- while evidence suggests that CR may support long-term skeletal health, weight loss is often accompanied by reduced bone mass, which may place you at risk of fracture. Work with your physician to monitor your bone mass and markers of resorption.
• cold sensitivity -- reduced body fat and decreased body temperature can make practitioners more sensitive to cold temperatures, while perhaps decreasing their sensitivity to extreme heat. Reduced fat can also make one's skin more sensitive to very warm or hot surfaces or liquids, such as hot tap water. This may put you at greater risk in case of unexpected, prolonged cold exposure -- such as after a car failure on the highway in winter.
• children, adolescents, and young adults (under approx 21) should be advised against starting CR. Physical growth may be impaired by calorie restriction, as observed in lab animals. In addition, mental development and physical changes to the brain take place in late adolescence and early adulthood that could be negatively affected by calorie restriction. For this group, the best advice is to follow a healthy, normal (non-CR) diet until reaching early twenties.
• loss of "cushioning" -- discomfort sitting on hard surfaces, etc., due to reduced body fat. Similarly, body tissues will be less protected from impact, leading to greater risk of damage to underlying tissues - such as bone or soft tissues.
• reduced energy reserves (due to less body fat) -- being unexpectedly stuck on a boat, locked in a room or lost in a wilderness are all scenarios where energy reserves may be important.
• hunger (both psychological and physical effects), cravings, or food obsession -- thoughts about food sometimes increase while practicing CR. For some, this may interfere with other aspects of their life.
• menstrual irregularity -- dramatic weight loss can sometimes interfere with reproductive function in women. Women planning to get pregnant soon, should not begin CR until after having (and weaning) their baby.
• pregnancy -- low BMI is widely regarded as a risk factor in pregnancy. It can result in ovulatory dysfunction and thus infertility. Underweight mothers have higher levels of preterm delivery - and more low birth-weight infants. Women planning to get pregnant soon, should not begin CR until after having (and weaning) their baby.
• loss of strength and/or stamina -- the weight loss on CR almost invariably includes some loss of muscle mass. This could be an issue in an emergency situation such as preventing a heavy object falling on you. This may also reduce performance in certain athletic activities.
• decreased testosterone
• rapid weight loss (greater than 1 - 2 lbs/wk) -- may do more harm than good, as noted in animal studies. We recommend changing your diet gradually, focusing at first on changing the quality of your diet: many people find that improving their diets by replacing low-nutrition, high-Calorie foods (such as sugar, grains, and high-saturated-fat) with high-nutrition, low-Calorie foods (notably fruits and vegetables) will lead to some weight loss even without any attempt to reduce Calories. Once your overall diet has improved, take at least six months to reach your stable weight or Calorie target.
• slower wound healing -- potential hazard in car accidents, violent attacks, surgeries, etc.

Synergistic interactions -- i.e. the combination of several CR effects

Lifestyle and Personal Impacts

Many peoples' practice of CR involves a great deal of their time and thought. This can take their time and thought away from other important aspects of their lives, such as people, hobbies and interests, and economic activity, and change their outlook on life.

Social Issues.

Eating food is often a social phenomenon. CR can sometimes interfere with conventional social practices...

• Family meals -- eating is often a communal activity, and a time for socializing with members of the family. CR can present some problems in this area:
  • Some CR practitioners try to eat less frequently than is usual
  • CR diets may not be suitable for all family members

  Such factors can work to divide and isolate family members -unless active steps are taken to combat their effects.

• Social events with food -- Many other types of social event also often involve eating:
  • Restaurants and bars
  • Parties, where hosts often offer food to visitors
  • Workplace lunches
  • Holiday season

Food and socializing are often intertwined; and not eating - or following unorthodox diets - can interfere with some aspects of a normal social life.

Time and Money

CR can be both a low-cost and relatively time-efficient regimen. For example: use frozen veggies or prepackaged salads; go for low-fat protein (turkey, canned fish, egg whites, soy and other meat substitutes or non-fat yogurt); add a dash of olive oil or a few raw almonds for fat; have an apple or orange for dessert; and, finally, take a generic multi-vitamin to make up for any deficiencies. However, achieving "optimal nutrition" can be time-consuming and expensive:

• Time
  • preparing meals (more than they would otherwise do)
  • swapping notes with other practitioners over the Internet
  • educating themselves about how best to practice CR
  • monitoring their health
  • seeking out a variety of foods and nutrients
  • growing their own food

• Money -- the health benefits suggest that CR should save on medical bills in the long run. However, it can involve expense on:
  • eating high quality foodstuffs
  • supplements
  • health monitoring equipment
  • consulting with physicians and/or extensive testing (many health plans may refuse to pay for certain tests in healthy individuals)

CR Psychology

CR represents a dramatic change in diet. This can attract people attracted to the extreme, who may push the limits of safe or healthy CR practice. Some anecdotal reports of CR-induced psychological disturbances include:

• anorexia
• binging
• excessive food thoughts and fantasies

While extensive scientific evidence suggests that CR may effectively slow aging, reduce the incidence of disease, and prolong life, CR practitioners should remember that CR is only a means to an end. Taken to extremes or practiced without due caution, unbalanced CR practice may result in a person losing his/her life in order to save it. Please note: The behaviors above, noted by various CR practitioners and one human study, are short-term and anecdotal. Long-term psychological repercussions of human CR are unknown. For further information, see Dean Pomerleau's well-researched presentation on the Psychological Effects of CR, originally given at the CR Society's 2nd Annual Conference (June 2003).

Additional information

This is by no means an exhaustive list. More information on specific topics can be mined from the Mailing Lists (search the archives). Use the descriptions above to narrow your search. Various books by Walford are also excellent resources. Notes:(1) CR means a reduction in intake of calories only. Just eating less food -- smaller portions of the food you typically eat -- will likely lead to malnutrition, rather than enhanced health. It's important to adjust your diet to ensure that intake of essential nutrients is maintained. Poorly-designed low-calorie diets are often low in calcium, zinc, iron, essential fatty acids, and protein. Fortunately, most people who practice CR find it quite easy to maintain proper nutrition for their age, sex, personal physiology and active lifestyle. The USRDA/DRI and Scientific American's New Food Pyramid may be used as a guide. Likewise, "yo-yo" dieting or "weight cycling" is not CR, but a far-too-common result of quick weight-loss diets. Some evidence suggests that yo-yo dieting may eliminate the beneficial effects of CR, or even be detrimental to health. If you find even minimal calorie restriction difficult, it is better to follow a healthy, non-CR diet.(2) Remember: despite the huge health/longevity improvements that CR potentially holds for humans it remains relatively "uncharted territory." Long-term physical and psychological effects are unknown. A CR lifestyle can involve (or necessitate, depending on the level of calorie reduction one wishes to pursue) carefully tracking calories, nutrients and physiological parameters (hormone levels, bone health, muscle/fat mass, etc.). As always, consult your doctor before making any dietary changes.