The math geek in me loves the way Tom Venuto (BFFM author) calculates caloric needs. There's no reason to drop very low - just 20% below your basal metabolic rate to start. Your BMR is the number of calories you need to survive if you're completely bedridden. There are some complex formulas to use, but a good guideline is your weight x 15. That gives you your maintenance level calories. For weight loss, the suggestion is your weight x 12. So, at 165 pounds, I require (165 x 15) 2475 calories per day just to lie in bed and (165 x 12) 1980 calories for weight loss. I'm not sure what the rate of loss is - maybe 0.5 to 1 pound per week. Of course, accounting for activity level will make a difference in the number of calories we can consume. But for starters, the information above is a good guide.
I complied some resources and created an Excel document that can be used to track measurements, food, and exercise for a 12 week challenge. Included in the document is a BRM calculator I found online. I'm not 100% certain, but I think I found it in a BFL Yahoo Group, so I can't give proper credit. . The BMR calculator also breaks down how many grams of carbohydrates, protein, and fat needed per day and meal. Based on this calculator, I need 2337.5 calories to maintain my current weight, with moderate exercise. The suggested number of calories for weight loss is 1870. That works out to 187 grams of carbohydrates, 187 grams of protein, and 41.56 grams of fat per day. At 6 meals per day, that's 31.17 grams of carbohydrates, 31.17 grams of protein, and 6.93 grams of fat per meal.
So, let's figure the numbers for a 40/40/20 ratio for low carbers. And let's round the numbers because even I'm not enough keep to eat a tenth of a calorie or gram!! So, let's say I need 2300 calories per day to maintain. The suggested 20% reduction in calories gives me 460 fewer calories per day - that makes 1840 - for weight loss. Of those, 40% (736 calories) will come from carbohydrates, 40% (736 calories) will come from protein, and 20% (368 calories) will come from fat. One gram of carbohydrates has 4 calories. One gram of protein also has 4 calories. One gram of fat has 9 calories. So, let's keep breaking down. The 736 carbohydrate calories per day works out to 184 grams of carbohydrates. Divide that by 6 meals and that gives me approximately 31 grams of carbohydrates per meal. Protein numbers will be the same. For fat, I need about 41 grams of fat per day, or 6.8 grams per meal. Wow, I guess the BMR calculator is developed on a 40/40/20 ratio! Sweet!!
But let's say I want to give myself a range of calories and give myself a 30% caloric deficit. With a BMR of 2300, 690 calories is 30%, so 1610 calories per day for weight loss. Crunch the numbers and I get 644 calories from carbs, 644 calories from protein, and 322 calories from fat. That's 161 grams of carbs, 161 grams of protein, and 35 grams of fat per day. By meal, 27 grams of carbs, 27 grams of protein, and 6 grams of fat.
So, now I have a range to aim for:
1610 - 1840 calories per day
27 - 31 grams of carbs and protein, 6 - 7 grams of fat per meal
On free days, 2300 calories, with 38 grams of carbs and protein, 8.5 grams of fat per meal.
I'm sure I made this much more complicated than it really is, but I love numbers!!