Now that you’ve determined your daily caloric needs, maximum carb limit and minimum protein requirements, the only other unknown is how much fat to include in your diet.
And this is where it gets interesting.
TWO SOURCES OF FAT
Once in ketosis, your body can use fat for energy. The key point to highlight here is that there’s actually two sources fat supply — body fat and dietary fat.
If you don’t want to use your own body fat, then all of your remaining calories need to be made up with dietary fat.
If you have spare body fat to lose, then your dietary fat intake needs to be less than your daily caloric requirements. Once in ketosis, your ketones will tap into your body fat to make up any caloric shortfalls.
LET’S DO THE MATH
Most keto calculators will do the ugly math for you, but it’s good to understand where those numbers come from. Using myself as an example, here’s what my math looks like:
- Given my height, weight and daily activity level, I’ve estimated my daily caloric needs to be about 1600 calories.
- I set my carb limit to 25 g/day to ensure I’m in ketosis. That works out to 100 calories/day[1].
- My protein target is 75 g/day. This is more than enough to sustain my muscles, and not enough to stimulate an insulin response. So my daily protein intake works out to 300 calories[2].
- The difference is therefore 1200 calories, which works out to 133 g/day of fat[3].
Since I’m not trying to lose weight, I therefore set my daily fat target to about 133 grams[4].
If I were trying to lose a small amount of body fat, I would lower that limit to 120 grams/day, leaving the remaining 13 g/day to come from body fat.
If I was looking to lose more weight more quickly, then I might lower my fat intake to just 100 g/day, leaving 33 g/day to be sourced from body fat.
Since I’m in ketosis, I’m able to tap into my body fat reserves when there aren’t enough calories in my diet[5]. This could be on purpose (if I’m trying to shed extra flab), or simply on a day when I did a heavy workout at the gym, or just didn’t eat enough.
A couple of important caveats on these calculations …
- This is obviously an oversimplification, since your caloric expenditure will vary from day to day due to activity levels.
- You might think eating a fat-free or low-fat diet would lead to very rapid weight loss. It might, at least at first. In the long run, your metabolism would suffer, lowering your daily caloric needs, which is not a good thing. It would also leave you feeling drained and lethargic, making the diet difficult to adhere to. So don’t go overboard with calorie deficits.
WAIT － YOU’RE NOT DONE YET! ONE MORE STEP TO GO …
Once you’ve set your numbers, it’s important to monitor body changes and adjust as needed.
As previously noted, your calculated daily caloric needs are just an estimate, and makes wide assumptions on activity levels and metabolism. As your body changes, your daily macro requirements will change along with it. It’s therefore very important to track intake, monitor results and adjust your macros as needed.
If you’re used to a high-carb diet, the transition to low-carb living difficult. Be sure to stick with it for a while, and not give up too easily. Give it a few weeks, and see what happens. But if it ain’t working for you, don’t be afraid to take a step back a re-evaluate. We’re all unique … what works for one person may not work for you. And that’s perfectly okay.
NOTES:
1 Carbs have 4 calories per gram. Be sure to exclude the fibre portion, which has no calories.
2 Protein also has 4 calories per gram.
3 Fat calories = Total daily caloric needs (1600) – carbs (100) – protein (300) = 1200 calories. Since each gram of fat has 9 calories, 1200 calories works out to 133 grams of fat (1200 ÷ 9).
4 Ketogenic diets are typically in the range of 5-10% carbs, 15-20% protein and 70-75% fat (percentages by calories). My macro ratio works out to about 6% carbs, 19% protein and 75% fat.
5 It’s worth repeating, you can only tap into your fat reserves if you’re in ketosis. If you’re not in ketosis, (for those on a more “conventional” diet), your body burns glycogen (sugar) for energy. As glycogen stores are depleted, your blood sugar drops, making you feel weak, prompting you to eat more carbohydrates to top up your glycogen stores. That’s part of the reason why fat loss is difficult when following a high carb diet, despite the reduction in calories.