Human Calorie Restriction:
Frequently Asked Questions
• What distinguishes CR from a weight loss diet?
Weight loss diets are aimed at shedding excess pounds,
either for aesthetic reasons, or to avoid the toxic health impacts of
obesity. These diets only make sense for people who are overweight.
By contrast, the goal of CR is slower aging and extended
lifespan. Weight loss is a side effect. In fact, CR’s anti-aging
effects manifest themselves even in organisms with a ‘healthy’
Weight change is, nevertheless, an easy and convenient
way of gauging one's overall Calorie intake. But, while it is worth monitoring
one's weight, it is important to remember that weight is just a proxy
for Calorie intake.
Please note: Increasing exercise, losing weight, and
keeping Calories unchanged is not what CR is about. An exercise regimen
that keeps you slim and leaves Calorie intake unchanged is not CR, but
simply a health program for weight control to slim down. top
• How low in weight can (or should) I go?
According to Walford, achieving 10 – 25% below
your current set point weight is considered reasonable. The definition
for “set point” is somewhat vague: "...that weight toward
which one naturally drifts." [Walford, B120YD.]. A safe CR weight
to strive for is generally considered to be your lean set-point weight:
your weight during late teens to mid-20s, providing you were not overweight
(e.g. obese) or underweight (e.g. anorexic) in your teenage years. top
• If I'm just starting CR, why shouldn't I lose weight as fast as
There are two basic reasons:
(1) In early experiments, CR failed to extend the lifespan
of adult animals, and sometimes even shortened it. It was Dr. Walford’s
insight that the reason for this lack of benefit might be that adult animals
were less able to adapt to this sudden change. In a groundbreaking study,
his team at UCLA were able to show that implementing CR gradually, with
especial care to ensuring the nutritional adequacy of the animals’
diet, led to gains in lifespan in adult organisms proportionately similar
to those observed in weanlings. Many other researchers have since confirmed
the efficacy of CR in adult organisms, but only when the restriction of
Calories is spread out over the human equivalent of a few years. top
(2) Our foods contain various chemicals (e.g. pesticides)
that are fat soluble. Throughout our lives, we tend to accumulate chemicals
in our fat as we eat commercially grown and processed foods. Most of these
chemicals are very slowly eliminated from our bodies when they are not
bound up in our fat. Therefore, losing fat (weight) too quickly will flush
lots of toxic chemicals into our bloodstream -- too fast for our bodies
to effectively eliminate. The result: dangerously high levels of toxins
circulating in our bloodstream and other tissues -- clearly undesirable
from a health and/or longevity perspective.
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In view of these reasons, humans should implement CR
over a span of one to two years, at the very least. top
• Where can I learn more about CR?
The best book for those interested in Calorie Restriction
the 120 Year Diet. Walford, Roy L. Four Walls, Eight Windows; (July
2000). ISBN: 1568581572
Anyone interested in pursuing a calorie-restricted diet
for the purpose of extending lifespan, or wanting to gain a basic understanding
of the scientific evidence supporting CR, should be familiar with the
information in this book.
Dr. Walford has also written two other books which are
• Anti-Aging Plan, The. Walford, Roy L. Four Walls
Eight Windows; (September 1995). ISBN: 1568580495
• Maximum Life Span. Walford, Roy L. W.W. Norton & Company;
(May 1985). ASIN: 0393016498
Dr. Walford endorses a high-carbohydrate, low-fat, low-protein
diet. However, the research shows that CR works with a wide range of macronutrient
ratios. For example, many people find the various "Zone"
diet books by Barry Sears useful.
Please be aware that although there seems to be significant scientific
support for most of Sears’ claims, the books are not well documented.
The CR Society email Archives
are a good place to find those references. The problem and the caution
is this: While most of Sears' information may be well supported, not all
of it is, and without specific references, it is difficult to differentiate
science from quackery. Therefore, before taking Sears' advice to heart,
make sure to confirm it by referencing the actual literature. For those
just starting CR, the best Sears Zone book is:
Sears, Barry. Week
in the Zone, A. Regan Books; (March 1, 2000). ISBN: 006103083X [CRON-WEB
See the Books section
for additional titles. For convenience, consult the CR Quick-Start Guide.
• Should I include fasting as part of my CR regimen?
The bottom line for practicing CR is eating fewer Calories.
If fasting helps you to reduce your caloric intake, you will probably
experience most of the benefits of CR. Studies have shown that rodents
fed all they can eat, but fasted every two, three or four days, also have
an increase in longevity, though the increase is not quite as great as
that of rodents on the standard kind of CR (when implemented in mature
For some people, this might be an easier way of doing
CR since hunger is limited to two or three days a week. Another option,
practiced by some, is to eat just once per day. The fasting method of
CR (when implemented in mature organisms), however, has not been researched
as thoroughly as normal feedings. It is possible that there are unknown
dangers to periodic fasting. top of page
• How does one reduce or control appetite or
otherwise adhere to the diet?
Some of the most time-tested ways of controlling hunger
and sticking with your goals are:
1. Filling up on bulky foods which are high in nutrients
but low in Calories -- such as most vegetables and fruits
2. Choosing carbohydrates with a low glycemic index
(GI) -- a measure of how quickly a food releases sugar into your blood
stream. Most starchy foods and dried fruits have high glycemic indexes,
while most vegetables and fruits are low-GI. For an extensive list of
foods’ glycemic indexes, see this link
3. Adding a little fat to a meal lowers the GI and releases
satiety hormones, which can help control appetite. On the other hand,
fat is a very Calorie-dense nutrient. Experiment with your diet to find
the right the balance for you.
4. Identify “problem” foods and either do
not keep them around, or buy a specific, small amount each week to enjoy
at a pre-determined time, as a reward for sticking to your CR eating plan.
5. Preparing and/or planning several days of meals ahead
6. Adhering to a daily meal schedule.
7. Eat your foods raw or only minimally cooked.
8. Enjoy your food: take the time to savor each bite
and chew thoroughly before swallowing.
9. Scientific reinforcements … almost weekly,
new research indicates that CR really works. Each new scientific demonstration
of the benefits of CR can strengthen your motivation! For example, here's
recent conclusive proof from the Washington University in Saint Louis:
"These effects are all pretty dramatic," said
Luigi Fontana, M.D., a research instructor and author of the study. "For
the first time, we've shown that calorie restriction is feasible and has
a tremendous affect on the risk for atherosclerosis and diabetes."
News Daily, 21 April 2004]
10. Social reinforcements … such as interaction
with members of CR Society
on the mailing list. Other CR practitioners can be a real source of emotional
support and practical tips, and most can attest personally to the tremendous
health and other benefits of CR! top of page
• What Do People on CR Actually Eat?
Lots of vegetables, some fruit, low-fat protein (e.g.,
lean beef, turkey or chicken, fish, low-fat dairy, soy and egg whites,
etc.) and good fats (e.g. nuts, avocados and olive oil). Just control
your total Calorie intake. It can be this simple!
See the Meal Plans section
of this site for suggestions. In addition, various books by Roy Walford
Barry Sears have excellent, low-Calorie suggestions – see this
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• How does one practice CR and good nutrition
when away from home?
Choose restaurants that offer healthy menu options. Many
health-food stores have attached eateries that offer nutritious choices,
but such foods are sometimes high in Calories because of added fats or
natural sugars. Be careful if the ingredients are not clearly spelled
out on the menu.
At fast-food places, choose salad bars, and fill your
plate with mostly veggies. For protein, go for egg whites, fish, chicken
or turkey breasts, low- or fat-free yogurt or milk. Use olive oil, vinegar
and pepper as dressing. More and more fast-food places are making the
caloric and other nutrition information available in their restaurants
or online; take advantage of these resources. Subway’s salads, 7
Low Fat Subs, and Low Carb Wraps made with ham, turkey, chicken breast,
tuna salad, seafood, or crab salad are a huge step toward true CR fast
foods. top of page
Parties and Holiday meals
If possible, follow the same “rules” as for
restaurants above. To reduce appetite, one can also pre-eat before scheduled
events. With company, one can then simply munch on servings from a vegetable
platter or other low-Calorie or healthy food options.
The bottom line is eating fewer Calories while assuring
adequate nutrition. Simply keeping one’s portions small, avoiding
second helpings or, perhaps, skipping one or more of your other meals
(before or after these events) are all strategies that CR dieters can
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• Are there any sample CR diets to help me construct
my own diet?
Yes… many good samples! See the Meal
Plans section of this site. In addition, the Books section
of this site -- it lists various books by Walford and Sears that
also have excellent, low-Calorie suggestions. top
• Are there any other ways of retarding biological
aging or extending lifespan besides CR?
None known to science at this time. Many interventions,
such as human growth hormone and other hormone “replacement”
therapies, as well as nutritional supplements and a variety of drugs,
are claimed by some people to be “anti-aging” therapies. These
notions are often plausible-sounding on their surface, and are attractive
because of their simplicity and ease of implementation. However as of
this writing, there is no reliable evidence to support the notion that
anything besides CR is capable of retarding biological aging or extending
maximum lifespan in adult mammals.
Of course, many basic health practices -- such as eating
a healthy diet and getting regular exercise -- can reduce your risk of
premature death. This is quite distinct from the genuine life extension
observed in hundreds of published scientific studies on CR.
We all want a quick fix rather than a rigorous regime.
More importantly, the best hopes for CR-induced life-extension are just
barely sufficient for the youngest of us to reach any sort of "clinical
immortality." Hence there are some researchers trying to develop
a "CR mimetic" – a drug that would mimic the effects of
CR without the need to cut one’s Calorie intake. However, no drug,
hormone, or supplement has yet been established as an effective CR mimetic
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