no weightloss with 800 calories a day!!!

800 calories is far too severe a restriction, especially because you are male (and presumably weigh more than ~90 lbs). By restricting calories so severely you're causing your body to go into starvation mode. This means that your metabolism slows down (making it harder to burn off fat) and the calories you do take in are far more likely to be stored as fat. Not only that, your body will often cannabilize muscle tissue over fat as it isn't being used and fat is a better energy storage cell, and your protein intake is usually very limited on such a diet (causing your body to eat its own muscle tissue to meet these needs). So in other words, "weight loss" is not really what you want. You want "fat loss." Muscle is attractive (to an extent), fat isn't. Being skinny fat is even less sexy (which is what this type of dieting will turn you into; a weak, sort of thin, but still fat, soft guy...not good). So what's the right way to determine how much to eat for weight loss, or rather how many calories to burn per day?
Well there are few formulas out there, there's the Harris-Benedict formula, which is based on total body mass (less precise but still useful if you aren't too overweight) and the Katch-McArdle formula which uses Lean body mass (more accurate, since this is the metabolically active tissue).
For example, a male who is 5'9" and weighs 180 lbs with a body fat of say, 25% (translates into 45 lbs of fat and 135 lbs lean body mass). Lean body mass is all of the metabolically active tissue in your body; muscle, organs, bone. Basically anything that isn't fat. To calculate this example male's resting metabolic rate we can use the Katch-McArdle formula, which goes as follows:
370 + 21.6 x Lean body mass in kilos. 135 lbs = 61.37 kilos, so 370 + 21.6 x 61.37 = 1695.6, in other words his basal metabolic rate would be about 1700 calories. Factoring in the minimal movement of a sedentary lifestyle (multiplying the BMR by 1.2) we get a figure of 2034 calories as this example's maintenance calorie intake level. In order to lose fat mass and retain/add muscle, he needs to create a deficit of 15-20% of total calories, and do resistance training to preserve muscle tissue and cardio to promote fat loss. However, keep in mind that calorie needs will go up if you are resistance training and doing cardio (which is the best way to lose weight and maintain that weight loss, and be healthier) so this 15-20% should be calculated from your calorie needs including the increase caused by regular exercise. Calculating calorie needs of exercise is a trickier matter which I'll have to leave up to you.
Also, what is in your diet is extremely important in weight loss. You need to eat a lot of whole, unprocessed and unrefined foods, plenty of proteins and healthy unsaturated fats (they won't kill you or make you magically gain weight...google it if you don't believe me).

Starvation mode is a myth, proven by several scientific studies that I currently do not feel like searching for. Do a search for it on Google yourself or, even better, in a medical database if you are lucky enough to have access to one. In one famous study, subjects consumed 800 kcal a day and 80g of protein, combined with resistance training 2 (or 3?) times a week, and lost some hefty fat and no muscle. However, don't confuse muscle preservation and drastic fat loss for a healthy diet. Such a drastic diet will likely cause moderate to severe physiological damage if used for more than a week.

Depending on your lean body mass, you should consume at least 1400 kcal a day (and then some, probably) to lose fat and keep your health in good order.

I was searching Google when I came up on this post and I wanted to clarify the issue for all of the confused dieters out there, all of you who are putting your health in danger or are just stumped by the 'mysterious,' seemingly mystical nature of physical conditioning. Who am I to give my two cents? Just know that I have significant schooling, experience, and make good money off of similar advice. You decide if it's right for you.

All the best,
Guest

I think I recall Oprah mentioning this diet and it worked for her. A diet that I suggest is to eat something every two hours. The trick is, you should only eat until you satisfy the hunger pain, and then stop. The reason you should eat to satisfy the hunger pain is because your body gives off sugar to satify the hunger pain. Have you ever known someone who doesn't eat a lot, but don't ever loose weight? Have you ever noticed that you may feel hungry, and then the hunger pain goes away? But don't over do it no matter how good the food is. Save the rest for the next two hours! Also, do not eat anything after 7:00 p.m (you should feel full from all of the eating). If you follow these steps, you should weigh the same amount when you got to sleep as you weighed when you woke that morning. Weigh yourself the next morning to see if you loss weight overnight. Sounds like a lot, but it's not. Think about it, you get to eat what you like and loose weight. Notice how fast you loose inches in the tummy!!

did you visit a nutritionist for that of kind of diet? You to consult first if it is effective to you... Others may effective to them but others not...
Cause i also try a lot of diet but none of them are effective to me... That is why i give up...

The reason why you arent seeing any change yet is that your body needs to get used to the fewer calories so for the first week, you probably wont lose any weight because ur body is holding on to everything you are putting in and by next week, u will see a change because ur body will start using up the calories u put in to keep you going. Stick at it. it will work.

Plus, do weights, or yoga and cardio for quicker results

Yes, I agree. Everyone's body reacts differently. But the diet of eating something every two or three hours really work. And you can eat whatever you want to eat; but only enough to curve the appetite! Probably would be a good to eat foods with low calories and fat, but you don't have to. People always tell me at work that I sit and eat all day, but never gain any weight. But this is the secret!!! Be sure not to eat pass 7:00 or 8:00 p.m. Good luck XD

I have been eating about 800 calories a day for the past 4 months ive since lost 4stone it does work i dont feel hungry any more, and its got to a point where i think i can do with out food im a little worried to be honest because i feel better for it n look better for it but will i ever be able to eat properly again

I need some help here. I'm 5' 8" female and I weigh 153 lbs. My goal weight is 135.
I'm wondering how this diet sounds.
WEEKS 1 and 2: mild exercise with a net consumption of 800 cal/day,
WEEKS 3 and 4: more intense workouts 3x a week with a net consumption of 1000
WEEKS 5 and 6: running 45 minutes 5x a week net consumption 1200 cal
WEEKS 7 and 8: 1200 cal with daily workouts
WEEKS 9 and 10: 1400 cal with daily workouts.....

How successful does this sound? I know going below 1200 cal/day isn't right for someone my height and weight, yet sometimes I feel like that amount is just more than I should eat to lose weight. I need specific recommendations from people who know about trimming up when you're already fit. My weight loss is only about 15 lbs but for some reason I've never been able to do it....I guess I just need some feedback.
THANKS!
K

P.S. Do active people's metabolisms recuperate from metabolic slowing faster?

I was diagnosed with hyperthyroidism when I was 20 I'm 27 most of it had to do with my heart then , now I have all the symtoms of hypo my blood pressure is low and, my heart rate seems normal, I don't have panic attacks anymore, I eat 600 to 1000 calories each day to maintain my weight I eat completely healthy an run on the elliptical once to twice a week this has been a routine for a 2 years now, I can not loose any weight no matter how hard I try , so iv had to work hard to just maintain it, what I'm asking is is it possible I was misdiagnosed or is it possible Changes over the years from hyper to hippo? Or am delusional

weight now comes in

stones

kilos

and pounds

so ????????????? what DO WE MULTIPLY ?BY 10

Things like this make me shake my head. You can lose weight by starving yourself but it's unhealthy and dangerous. If you really aren't very educated on weightloss you will not make progress. Please go on youtube and search "scooby weight loss" and click on the first result. 

Just stick to 800 calories of whole foods no sugar or anything white,

I did a 800 calorie diet for 6 weeks with one day out the week to eat 1 meal of whatever i wanted and lost 25 lbs after 4 weeks. The trick is to maintain certain food, i mostly ate veggies and a protein once a day, usually at dinner in portion size. I was also working out 5-6 times a week for 30 minutes and doing a small amount of weight lifting. Also I used multivitamins to help with the nutrition i wanted and if i craved something sweet ate like 1/5 of a serving instead of a full serving.

I eat the following and I have no hungry. I make a big pot of vegetable soup. It is only 100 calories for two cups of soup. A small orange is 65 cal. an apple is 79 cal. 2 oz. of cheddar cheese is 208 cal. You can eat all the salad and raw vegetable you want to. Use only a tsp. of olive oil and apple cider vinegar. Raw vegetables are unlimited. You can use herbal tea and decal coffee in between meals. Remember the body takes 6 hours to use up the glucose in your meal. So I eat between 8:30am to 2:30pm and quit for the day. If I do get hungry soup or raw vegetables do the trick.