Basics of Diet and Weight Loss

101 of the math behind diet and losing (or gaining) weight

Writing my mental model out loud, I am not an expert. If you are an expert and think that I have made a mistake, please reach out and correct me.

To lose 1kg, you approximately have to be in ~7700 calorie deficit. For simplicity and to be on the “safer” side, I will use 8000 calories = 1kg weight loss. TK source

Example numbers for my use case:

• Weight: 72kg

• Body Fat Percentage: 24%

• Lean Mass (weight - fat): 72 - 24% of 72 = ~55kg
  (note, this includes bones)

• Basal Metabolic Rate: 55 * 30 = 1650 calories
  (or resting energy or daily calorie intake to maintain the weight)

• Active Energy (Daily Average for 1 Year) = 600 calories

• Total Daily Energy = 1650 + 600 = 2250 calories

• Weight Loss Goal: 0.5kg / week = deficit of ~570 calories / day

• Calorie Budget per Day = 2250 - 570 = 1680 calories

I was 78kg at the beginning of this year! Also documenting my experiments on Twitter:

Follow here:

https://twitter.com/divyenduz/status/1609546345076883456

Screenshot of the Twitter link

Gotchas / Other Things / FAQ

1. To lose 0.5 kg (a sane speed) in a week, you need to lose around 4000 calories which is being in a deficit of ~570 calories per day.
   
   Why sane speed? because if you do it too quickly, your body slows down the metabolic rate
   

2. Body fat percentage → mine is based on InBody scan, DEXA scan is more accurate. But if you have nothing available, there are crude methods available.
   

3. Why multiply lean body mass by 30 calories to calculate basal metabolic rate? It is based on the book exercised

   

4. Calorie math goes like this
   1g carb = 4 calories
   1g protein = 4 calories
   1g fat = 9 calories
   1g alcohol = 7 calories (safe to treat it like fat) TK source
   

5. Glycemic index → some foods are broken down slower than others, make you feel more satiated. If you are more satiated, you eat less. Fat has a high glycemic index
   

6. balanced diet → don’t try to skip fat totally or be leaned towards one macro nutrient.
   
   Besides macro nutrients, a balanced diet also helps with various micro nutrients that the body needs
   

7. Hard things about counting calories → food labels can be +/- 10% off, weighting everything is hard, not all food is calorie counted, hidden calories (like sauces etc.)
   

8. Hard things about resting energy → it changes, specially if you shift your diet drastically. Apple watch and many online tools calculate it incorrectly because they use non-lean mass (see point 2)