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Why is a 666 calorie diet not right?


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Well, I checked online and a 5'2" 31 year old male that weighs 123lbs should consume about 1500 calories per day... I saw on the main page that mice were fed a 65% CR diet... I really want to start eating only 666 calories per day starting in six days (6/16/16)... Why is this wrong? (I've posted on this before and still don't see why it's wrong... If mice can do it why can't humans?) btw... I absolutely *love* the way I feel when I restrict my calories... It seems the less I eat the better I feel!


Let me know what you guys think...



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Sthira, don't joke about stuff like this.




I hope you are joking with all the 6's, but it's dangerous to promote such an idea as cutting calories to 666kcal/day, even in jest, since many different kinds of people read these forums - including anorexics looking for validation. I presume (and hope) you aren't one of them, but just in case you are, or anyone else reading this is, here goes...


A person cutting calories by 65% and maintaining that level for years (which is what I assume you mean - not a temporary fast) is ludicrous for so many reasons. I'm just going to list a few without references. Sorry, I don't have the time or the inclination to indulge such self-destructive craziness:

  • Early Mortality - Yes, some of the severely restricted mice live a long time. But it is quite common in rodent CR experiments for members of the CR group to much die earlier than the AL group, particularly when extreme degrees of CR are employed.
  • Early Onset Required - The Weindruch experiment where 65% CR was shows modestly more effective than other levels of CR, the mice were started on CR shortly after weaning. Adult onset CR has never been shown effective at 65% restriction.
  • Gradual Onset Required - In adults rodents, even more mild CR has only been consistently shown effective when gradually introduced to the animals - over a stretch of time equivalent to several human years. Dramatically dropping calories next week would be foolish even if it didn't entail quite so insane a degree of restriction as you are talking about.
  • Diminishing Returns - Time and again it has been shown that more extreme CR isn't required to achieve most of CR's benefits. See this thread for discussion & evidence.
  • Negative Side Effects - Bone health. Sarcopenia. Compromised immunity etc. I seriously doubt it for all the other reasons listed, but perhaps you could live a long time at CR65 if you lived in a isolated, germ-free cage. But we live in the real world.
  • Restriction Relative to Ad Lib - The 65% CR success was relative to ad lib feeding of mice. When fed ad lib, mice become obese. A 5'2" man eating 1500kcal/day is not going to get obese. To get obese you'd probably have to eat 2500-3000kcal/day and do no exercise. Even then it might not happen. So the equivalent of 65% CR in a man like yourself would be relative to a much higher caloric baseline if it were to be equivalent to the 65% CR rodent result, so much higher than 666 kcal/day.
  • Exercise Burns Calories - If you want to avoid the negative side effects of CR on bones and critical muscles (e.g. like your heart) you need to exercise. On 666 kcal/day that won't be possible.
  • Basic Nutritional Requirements - I challenge you to put together a healthy diet that can meet your nutritional needs on 666kcal/day without excessive supplements, which we know aren't sufficient or equivalent to getting nutrients from whole plant foods.

I hope those are enough reasons for your or anyone to recognize how crazy dropping to 666kcal/day would be.


Don't do it unless you've got a deathwish. If this is the case you shouldn't be here, but instead you should be seeking psychiatric help. In the US, the nationwide, toll-free suicide hotline is 1-800-273-8255.



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Fred, in addition to everything Dean has said, let me add this: your proposed diet is based on faulty assumptions. I know that we were all inspired to do CR based on rodent studies, but I think it has always been recognized that rodents are not humans, and we can't extrapolate dietary recommendations exactly 1:1. Different animal species have different basic (i.e. minimal) caloric requirements. As just one example, many birds eat stupendous amounts we could never hope to equal no matter how hard we try. Human homo sapiens sapiens bodies are not just rodent rodentia murinae rattus bodies scaled up. They are different physiologies operating differently needing different amounts of calories. Furthermore, we now have contradictory evidence - at best - as to whether CR works in humans at all (and Dean has even made some good points wrt. CR in rodents too!). At those levels of caloric intake you will damage yourself, no question (if you sustain it for any length of time) - you will catabolize vital internal organs, including your heart. That way lies madness, not optimal health. Desist from that plan.

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I thought the OP was joking. What's with the repetition of numeral six if not some biblical ref? No one will ever acheive some exact caloric number anyway, people, it's all guesstimation. Every blackberry has a different number, every consumer scale is not quite on it. These numbers on cronometer, I take them as ballpark estimates and not as, um, revelation gospel.

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FWIW, Michael agrees with us about the impossibility of this degree of CR, saying in this recent post (emphasis his):


[N]o free-living human can possibly tolerate 50% CR. 55% CR is on the razor's edge of lethal to experimental rodents, who never have to sprint or really do much of anything involving substantial energy output if they don't want tot; no organism could possibly voluntarily adhere to something that close to the edge for long.



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Thanks for the help guys... I wanted to do 666 calories/day because I thought you'd live longer if you did that and yes it was because the date is 6/16/16... I was going to do 666 cals/day in 2016, 700 cals/day in 2017, 800 cals/day in 2008 and 999 cals/day in 2019 then go back to 800/day in 2020... I'm actually glad to hear that if you want to exercise it's good not to severly restrict calories... Why? Because I love the treadmill... the runner's high is incredible... I really want to stay young-feeling and fit my entire life and want to do everything I can to maintain a youthful appearance... If you look at pictures of 70 year old's, the individuals who exercise are so much younger looking... I hope to be like that one day...


Can anyone tell me how many calories a person my height 5'2" and 123lbs (I am not there yet but once I do I want to maintain that weight) can eat as a minimum if I run 20 minutes on the treadmill per day and lift weights -- nothing excessive though... I am really into this calorie-restricted thing... I'm telling you, back in 2009 when I tried calorie restricted for the first time (I weaned myself onto it)... I felt amazing... really... I now weigh 220 lbs and am working with a nutritionist  losing about 2lbs of fat per week... it's still so hard to believe that by the end of the year I might be thin again... It's been a while since I could look at myself in the mirror and not be disgusted...


Thanks for your help, guys...

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I'm glad you enjoy exercise and are no longer considering such a tremendous degree of restriction. Just to further discourage your or anyone else thinking about such extreme measures, here is what 65% calorie restriction (w/o good nutrition, which is impossible at that level for people):




That is a photo of Rachael Farrokh, who has been fighting anorexia nervosa for 11 years. She published this photo along with her story in order to obtain medical treatment. Thank goodness, she is still alive, but she will likely be struggling with anorexia for her entire life. You don't want to go there.

Can anyone tell me how many calories a person my height 5'2" and 123lbs (I am not there yet but once I do I want to maintain that weight)

It's very hard to say how many calories someone who is 5'2" and 123 lbs would need to maintain weight while exercising modestly. It all depends on your metabolism when you get there (see below), as well as the diet composition (e.g. how much fiber, etc). No big deal. You'll just have to adjust your calories when you get there. 
About getting there. You've obviously got a long way to go, and it's great you're working with a nutritionist and thinking ahead. I worry that targeting 2lbs of fat loss per week is too much too fast, even for someone with as much weight to lose as you have. In addition to the toxin release issue, rapid weight loss creates the potential for adaptations by your metabolism that will make it more difficult to maintain a lower weight in the long run. This was highlighted recently in a study [1] of contestants on the TV show "The Biggest Loser". The contests, who all lost a large amount of weight quite rapidly, had a lower metabolic rate at the end of the competition than at the beginning, which isn't surprising since it takes energy to maintain all that fat, and because they lost metabolically active muscle along with all that fat. But here is the kicker. After six years, nearly all of them had regained most of the weight they had lost but there metabolism remained suppressed - meaning they had to eat less than they were eating before the competition to avoid getting fatter than when they started.
You certainly don't want to end up like one of Biggest Losers, with a metabolism that makes it almost impossible to avoid obesity. Some of that involves losing muscle mass, which can be mitgated with exercise. But some of it appears to result from simply losing weight too fast. So that's one more reason to keep your weight loss slow and steady.


[1] Obesity (Silver Spring). 2016 May 2. doi: 10.1002/oby.21538. [Epub ahead of

Persistent metabolic adaptation 6 years after "The Biggest Loser" competition.
Fothergill E(1), Guo J(1), Howard L(1), Kerns JC(2), Knuth ND(3), Brychta R(1),
Chen KY(1), Skarulis MC(1), Walter M(1), Walter PJ(1), Hall KD(1).
Author information: 
(1)National Institute of Diabetes and Digestive and Kidney Diseases, National
Institutes of Health (NIH), Bethesda, Maryland, USA. (2)Hospitalist Section,
Washington DC Veterans Affairs Medical Center, Washington, DC, USA. (3)Department
of Kinesiology, Towson University, Baltimore, Maryland, USA.
OBJECTIVE: To measure long-term changes in resting metabolic rate (RMR) and body 
composition in participants of "The Biggest Loser" competition.
METHODS: Body composition was measured by dual energy X-ray absorptiometry, and
RMR was determined by indirect calorimetry at baseline, at the end of the 30-week
competition and 6 years later. Metabolic adaptation was defined as the residual
RMR after adjusting for changes in body composition and age.
RESULTS: Of the 16 "Biggest Loser" competitors originally investigated, 14
participated in this follow-up study. Weight loss at the end of the competition
was (mean ± SD) 58.3 ± 24.9 kg (P < 0.0001), and RMR decreased by 610 ± 483
kcal/day (P = 0.0004). After 6 years, 41.0 ± 31.3 kg of the lost weight was
regained (P = 0.0002), while RMR was 704 ± 427 kcal/day below baseline (P <
0.0001) and metabolic adaptation was -499 ± 207 kcal/day (P < 0.0001). Weight
regain was not significantly correlated with metabolic adaptation at the
competition's end (r = -0.1, P = 0.75), but those subjects maintaining greater
weight loss at 6 years also experienced greater concurrent metabolic slowing (r =
0.59, P = 0.025).
CONCLUSIONS: Metabolic adaptation persists over time and is likely a
proportional, but incomplete, response to contemporaneous efforts to reduce body 
© 2016 The Obesity Society.
PMID: 27136388
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