I've been doing a very low carb ketogenic diet the past couple weeks and revisiting some of the nutritional theory that floats around the internet under the name of diet advice.
For many years I have used nutritional software and a food scale to track and log my food intake when I diet, so I have a very good idea of what I'm eating. But recently I've gotten curious about the impact of macronutrient balance: how much of a difference it makes when we change the proportions of protein, carbohydrate and fat that total up to a given caloric intake.
When we cut carbs, we know we have to raise our protein intake high enough to provide the raw material from which the liver can synthesize the glucose it needs to run the brain--the only organ that requires some glucose to keep running. At the outset of a ketogenic diet the brain requires about 100 grams of protein.
We also know--though many supposedly trained nutritionists do not--that after three weeks on a ketogenic diet, the brain's requirements for glucose drop significantly--to about 40 grams a day--as it ramps up to run on ketones instead.
(This last phenomenon is why children with certain kinds of epilepsy are able to eat extremely low carbohydrate diets for years at a time and heal their brains.)
Our bodies also need dietary protein to repair our muscles. There are formulas we can use to calculate how much extra protein we need for this function.
If we eat enough protein, our bodies will not cannibalize lean muscle as we diet. So getting adequate protein is essential to healthy dieting. But there are limits to how much protein we should eat: too much protein will not only stall weight loss but will produce the unpleasant "diet breath" that many dieters erroneously attribute to ketones. In addition, excess protein can turn into glucose and raise blood sugar. So our goal when dieting should be to eat only as much protein as we actually need.
Once we know how much protein and carbohydrate we are going to be eating, the next question we need to ask is how many calories we want to eat. The traditional diet advice is to calculate your resting metabolic rate (BMR) --the amount of energy you use just breathing, digesting, and pushing blood around your body, and add to this the amount of calories burned by activity.
Many formulas exist to estimate the BMR, though they work best for large populations, not individuals. I reviewed the research that tested these formulas against actual measured BMRs, and it looks like the formulas that do the best job at estimating BMR in real people are the Mifflin-St Jeor formulas.
It turns out that the Harris-Benedict equations that many web sites use in their calculators were developed in the early 1900s and err by 18% when tested in the lab. They often overestimate calories burned and dieters who use them to set caloric goals may end up overeating.
Once we know how many calories we are supposedly burning, we can, in theory, lose a pound a week by eating 500 calories less than we are burning. This allows us to set a calorie goal.
Once we know how many calories we want to eat, we can calculate how much fat we can add to our previously computed protein and carbohydrate intake to come up with a final macronutrient prescription.
I've put together a calculator that will compute your own macronutrient prescription using the principles just outline and I'm inviting you to test it out.
The calculator is only designed to prescribe macronutrients to people on a ketogenic low carbohydrate diet, defined arbitrarily as one that does not exceed 80 grams of carbohydrate a day. It is only for adult use and should not be used by people older than 75 whose BMR is not calculated properly by the Mifflin-St Jeor formula.
It prescribes a nutrient breakdown for both maintaining your weight and for losing weight. However, no matter what your metabolic needs. It will not prescribe a diet of under 1100 calories a day out of a belief that eating below that level may unduly slow our metabolisms.
I put this calculator forth understanding that many people eating very low carb diets find it possible to eat more calories than nutrition formulas predict and still lose weight or maintain weight. Turn to this calculator if you are stalled.
This is a beta version. I'd be very interested in hearing from those of you who track your nutrients how well the calculator's prescriptions match your own experience with successful weight loss.
For those of you who are stalling on your diets, I'd be very interested in hearing whether using its prescriptions can help you break your stall.
Here's the link to the calculator:
Calculate Your Nutrient Balance on A Ketogenic Low Carbohydrate Diet
Please post your feedback about the calculator in the comment section of this post.
Thanks!
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