This is an interesting question, and probably more complicated than I can tell with my "enough knowledge to be dangerousness". If we are in a state of lipolysis (burning fat for energy) and a pound of fat contains 3500 calories, then what is the reason for food intake? Most of us have plenty of energy to live on for quite a while. I can think of 4 things... replenish glycogen, replenish micronutrients, supply amino acids for tissue repair/growth, and supply fatty acids for cell repair, vitamin absorption, and other normal functioning.
First, according to http://www.answers.com/topic/glycogen , "In a healthy adult, the liver glycogen store is usually between 50 and 100 g, containing enough glucose to satisfy the brain's requirements for up to 24 hours."... 100x4 is 400 calories from carbs.
Also, according to http://www.answers.com/topic/glycogen , "In an adult there are about 250 g of glycogen in the muscles."
That brings up exercise. Again from the same article, "With low intensity exercise (such as slow walking, cycling, or swimming) the muscles do not use much glycogen as they are able to take up fat from the blood as a source of energy for contraction. However, with higher intensity exercise (jogging, brisk uphill walking, running) the muscles need to use glycogen or glucose from the blood to support the higher rate of energy expenditure."
So if you're an endurance athelete, you might use (for example) 150 grams of muscle glycogen per day. 150x4 is 600 calories of carbs.
600+400=1000 calories from carbs or 250g of some type of sugar...IF YOU'RE LARGE AND EXERCISE VIGOROUSLY EVERY DAY.
USDA recommends up to 70g of protein a day. Exercise really has little to do with how much protein you'll need, but to be on the safe side we'll take in 100g of protein for an avid weightlifter. Add 400 more calories for a grand total of 1400 calories so far.
Which brings us to fats. I used to have a doctor who would put everyone on a diet where you couldn't eat more than 20g of fats per day. I'm assuming that 20 grams of fats can give you enough to repair nerves and cell walls for the day. I know this isn't the usual fat intake, but Fast-5 isn't the usual diet. ;) So 20x9 is 180 calories from fat. 1400+180 is 1580 calories.
1580 calories a day for a big, burly, marathon training athelete who is on Fast-5.
Obviously, I've created my example human out of thin air. A small woman for instance who works in an office would hardly ever empty her muscle glycogen supplies. So she could subtract 600 calories giving us 980 calories, and she sure wouldn't need all that protein so we could get her to live on 50g of protein a day. So subtract 200 calories and we end up with a person who could live on 780 calories for maintenance.
But like Daniel mentioned, once your bodyfat gets rather low, you would need to get more food from outside sources.
This also underscores the importance of eating more nutrient dense food as you decrease the amount of calories you take in.
Also, take into account that your body takes about 3 days to metabolize the food you take in today. So if you've gained a pound, try to remember what you ate 3 days ago.
I guess what I'm trying to say here is that it totally depends on the size and activity level of the person as to how many calories they can get away with. I HAVE seen a couple of studies that gave a group of women 800 calories a day for 3 months, some exercised, some didn't. They all lost HUGE amounts of weight and stayed perfectly healthy.
Sorry for the length, but it is a complicated question and I've thought about it a lot. I'd love to hear other's opinions on this.
-Rick Stewart
--- In fast5@yahoogroups.com, "Daniel Lurie" <dl1021@...> wrote:
>
> On Wed, 13 May 2009 08:51:55 -0400, Cassie Luu <cdluu@...> wrote:
>
> > is there a minimum number of calories/day that we should be striving for?
>
> Going below 10 cals/lb/day is generally a bad idea unless you have a huge amount of bodyfat.
>
> The leaner you are, the less of a calorie deficit you can tolerate.
>
> --
> Thanks,
> Daniel Lurie
>
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