0:00:03.187,0:00:07.704 So let's talk about body mass index (BMI). 0:00:07.704,0:00:15.903 This is a term that's often discussed and so let's first figure out how it's calculated - how do we figure this out? 0:00:15.903,0:00:23.719 So, if you have a little stick person, what you could do is have them step on a scale. 0:00:23.719,0:00:27.754 And you could get their weight. So, the first thing you need is their weight. 0:00:27.754,0:00:33.237 And then you go on and you ask them if they would mind if you would take their measurement of height. 0:00:33.237,0:00:36.453 And so you get their "H" or height. 0:00:36.453,0:00:44.052 And a BMI is basically just taking those two numbers and using them in a little equation 0:00:44.052,0:00:49.519 where you take the weight divided by the height squared. 0:00:49.519,0:00:51.986 Very simple, right? 0:00:51.986,0:00:55.104 So now, let me calculate my BMI. 0:00:55.104,0:00:57.204 But before I do that, I have to tell you one more thing 0:00:57.204,0:01:03.220 Which is that, the weight, this is in kilograms (kg) 0:01:03.220,0:01:08.136 and the height is actually in meters squared. 0:01:08.136,0:01:11.038 So, when I was actually figuring out my own height and weight 0:01:11.038,0:01:13.253 I realized the problem and I'll show you what that was. 0:01:13.253,0:01:23.736 So, my weight is 160 pounds and my height is six foot, one inch. 0:01:23.736,0:01:27.769 Which is the same as 73 inches. 0:01:27.769,0:01:33.586 So, I would love to use this easy equation, but I have pounds and inches - I don't have kilograms and meters. 0:01:33.586,0:01:38.387 So what do I do? Well, what I need to do first is convert over, right? 0:01:38.387,0:01:51.419 So I can say, "Alright, well one pound equals 0.454 kilograms. So far, so good. 0:01:51.419,0:01:59.705 And now one inch, which is pretty small, is going to be a small number relative to a meter, which is huge, right? 0:01:59.705,0:02:09.786 And so, it is, it's 0.0254 meters." 0:02:09.786,0:02:16.053 So, now I've got my conversions and actually, what I can do, is I can take these numbers and plug them in here 0:02:16.053,0:02:23.602 to help me easily convert from kilos and meters over to pounds and inches - make my equation much simpler for me to use. 0:02:23.602,0:02:34.685 So I can say, "Okay, well now how about weight in pounds and height in inches squared?" 0:02:34.685,0:02:36.286 And I have to multiply, right? Because I have to multiply by the conversion. 0:02:36.286,0:02:52.870 And so, I'll multiply by 0.454 divided by 0.0254 squared. 0:02:52.870,0:02:58.720 And to make it even easier, I can actually take this whole thing, plug it into my calculator 0:02:58.720,0:03:07.203 and it gives me the number 703. So I can say, "Okay, so really what I have here is, again, weight in pounds 0:03:07.203,0:03:17.387 divided by height in inches squared, multiplied by 703." 0:03:17.387,0:03:20.704 So going back now, I can finally throw in my own numbers, right? 0:03:20.704,0:03:45.053 I can say, "Okay, so my BMI is 160 divided by 73 squared times 703." 0:03:45.053,0:03:47.154 Let me erase that just to make it clear. 0:03:47.154,0:03:51.270 Okay, so this math works out to 21. 0:03:51.270,0:03:53.503 So my BMI is 21. 0:03:53.503,0:03:56.302 Wonderful. The next question is: well, what does that mean? 0:03:56.302,0:04:04.102 You know, if I have a BMI of 21, is that normal or is that good or how should I feel about that? 0:04:04.102,0:04:09.620 So, if you put a scale on here starting with zero to, let's say 30 0:04:09.620,0:04:18.219 and I have 25 here and let's say this is about 18.5 0:04:18.219,0:04:23.453 What physicians have done is basically divide up the BMI into catergories 0:04:23.453,0:04:30.387 and they said, "Okay, well if your BMI as an adult is somewhere between zero and 18.5 0:04:30.387,0:04:34.852 somewhere in this range. I'm going to do it in yellow. 0:04:34.852,0:04:44.219 Then you're underweight. I'm just going to write "under." And if you're between 18.5 and 25 0:04:44.219,0:04:49.686 if you're in this range, you're in a very healthy range. 0:04:49.686,0:04:53.502 And so I'll write a little smiley face for that. 0:04:53.502,0:04:59.569 And if you're above 25, let's say 25 to 30, then you're in the overweight range. 0:04:59.569,0:05:07.937 And finally, if you're above 30, let's say you're out here, then you're obese." 0:05:07.937,0:05:11.753 And so that's where the word obese really comes from. 0:05:11.753,0:05:15.053 It comes from a category of BMI. 0:05:15.053,0:05:19.519 And so, going back to my BMI, I'm right here at 21 0:05:19.519,0:05:24.369 and I'm doing pretty well. But, the question might come up in my head, 0:05:24.369,0:05:30.086 "What weight would I be if I was overweight and what weight would I be if I was obese? 0:05:30.086,0:05:34.236 How many pounds away am I from being in those categories? 0:05:34.236,0:05:38.103 So I can go back to my equation: 0:05:38.103,0:05:41.803 BMI equals W over H squared and I can just rearrange it 0:05:41.803,0:05:55.320 I can say, "Well how about W equals BMI times H squared over 703, right?" 0:05:55.320,0:06:00.587 Because that's the conversion. So if I rewrite the equation like this 0:06:00.587,0:06:07.288 then now I can solve for my weight. I can say, "Okay, well let's say that I wanted to figure out what to do 0:06:07.288,0:06:14.370 if I have a BMI of 25 and I know that my height probably won't change, 0:06:14.370,0:06:22.404 I'm not going to grow anymore and 703 is the number we always have to use when we're using the conversion from 0:06:22.404,0:06:27.188 pounds to kilos and inches to meters. So, what does that equal? 0:06:27.188,0:06:38.370 Well, in this particular case, using 25, I can see that for me to be overweight, I would be around 190 pounds. 0:06:38.370,0:06:43.852 190 pounds. So that's actually really, really good to know 0:06:43.852,0:06:46.737 That's actually 30 pounds above what I am today. 0:06:46.737,0:06:52.253 So that gives me a sense for how far away I am from being overweight 0:06:52.253,0:06:57.610 and I can even do this for a BMI of 30. 0:06:57.610,0:06:59.609 I can say, what about a BMI of 30? 0:06:59.609,0:07:04.710 My current height, again, is 73 inches. That's not going to change. 0:07:04.710,0:07:14.394 And I can do the math and find out that, in this case, my weight would be 227 pounds. 0:07:14.394,0:07:18.394 So if I was 227 pounds, given my height, I would be considered obese.