religions use periods of fasting as a means of demonstrating faith or
penitence, and an opportunity for spiritual reflection. Fasting has also
historically been a means to express political views and a form of
Though it may
not be the most practical -- or safest -- diet, some people use fasting
as a way to lose weight or to cleanse the body of toxins, although some
experts say our bodies are perfectly equipped with organs that already
do the job. How fasting is used for weight loss varies by diet. Some
fasting diets involve drinking nothing but water or eating only raw
foods for a period of one or more days, while others restrict food on
alternate days. Certain fasting diets only allow liquids like water,
juice, or tea, while others dramatically cut calories but do not
eliminate food altogether.
Does Fasting Help You Lose Weight?
you fast, your body is forced to dip into energy stores to get the fuel
it needs to keep going, so you will lose weight. The big question is
how long you will keep that weight off. Because food was often scarce
for our ancestors, our bodies have been genetically programmed to combat
the effects of fasting. When you eat less food, your metabolism slows
down to conserve energy. Then, when you go back to your usual diet, your
lowered metabolism may cause you to store more energy, meaning that you
will probably gain back the weight you lost and possibly even put on
more weight when eating the same calories you did before the fast.
you fast, your body will adjust by reducing your appetite, so you will
initially feel less hungry. But once you have stopped fasting, your
appetite hormones will kick back into gear and you may actually feel
hungrier and be more likely to binge.
Research has shown that
fasting on alternate days can help people lose weight, but not for long.
In one study, people who followed an alternate-day fasting diet shed
weight, even when they ate all they wanted on the nonfasting days.
However, they could not maintain the weight loss over time.
Can Fasting Detoxify the Body?
fasting diets claim that they can cleanse the body of impurities.
However, there is no evidence that fasting detoxifies your body, or that
your body even needs to be detoxified. It is naturally designed to
remove toxins through the skin (by sweating), liver, colon, and kidneys.
Could Fasting Help You Live Longer?
of fasting in both rodents and humans appear to indicate a connection
between calorie restriction and longevity. In one study of overweight
men and women, a calorie-restricted diet improved markers of aging, such
as insulin level and body temperature.
Fasting might also improve
longevity by delaying the onset of age-related diseases including
Alzheimer's, heart disease, and diabetes. One study showed that skipping
meals once a month, as members of the Mormon religious group do,
reduces the risk of clogged arteries (the build-up of plaque that can
lead to heart attacks and strokes). However, it is not clear from this
research whether fasting alone or the Mormons' generally healthier
lifestyle (they also abstain from coffee, alcohol, and smoking) is
responsible for the improved heart health.
Researchers do not
yet know whether the effects of fasting translate into an actual
increase in lifespan, because they have not followed people for long
enough periods of time. However the concept of intermittent fasting,
such as skipping a meal purposefully on an intermittent basis, is
gaining attention. It appears to be a relatively safe way to reduce
caloric intake that is easier for some people to do. The data however is
not there yet nor is this an accepted practice.
Is Fasting Safe?
for a day or two probably won't hurt people who are generally healthy,
provided they maintain an adequate fluid intake. However, fasting
entirely for long periods of time can be harmful. Your body needs a
variety of vitamins, minerals, and other nutrients from food to stay
healthy. Not getting enough of these nutrients during fasting diets can
lead to symptoms such as fatigue, dizziness, constipation, dehydration,
gallstones, and cold intolerance. It is possible to die if you fast too
Even short-term fasting is not recommended for people with
type I diabetes, because it can lead to dangerous dips and spikes in
blood sugar. Women who are pregnant or breastfeeding, or anyone with a
chronic disease, should not fast.
Before you go on any type of
new diet, particularly one that involves fasting, talk to your doctor to
find out whether it is safe and appropriate for you. Also ask your
doctor to refer you to a registered dietitian, who can show you how to
design a healthy eating plan.