There Ain’t No Such Thing As A Free Lunch

You see a lot of interesting claims, when you’re trying to lose weight.  One of them is the idea that there is a such thing as calorie neutral food or even food that requires more calories to digest than you reap from digesting it.  On the surface, this seems reasonable.  After all, it takes energy to secret acids and generate mucous and make the stomach agitate your food, so some foods should consume more energy than they produce.  Right?

Well, with nutrition as with so many other things, what sounds reasonable isn’t necessarily accurate.  Let’s start with the definition of a calorie:  the approximate amount of energy needed to raise the temperature of one gram of water by one degree Celsius at one atmosphere of pressure.  A dietary calorie is the “large calorie” or “kilogram calorie”, and is the amount of energy required to raise the temperature of one kilogram of water by one degree Celsius at one atmosphere of pressure.

How much energy does it take to digest something?  It turns out that there’s a thing called the thermic effect of food.  Science Learning describes it like this:

“It takes energy to metabolise foods. For example, carbohydrates and fats have a thermic effect of about 5% whereas protein is about 30%. This means that, to metabolise 100 kilojoules of carbohydrate, 5 kilojoules is needed, leaving the body with 95 kilojoules of useful energy. In comparison, to metabolise 100 kilojoules of protein, 30 kilojoules is needed, leaving the body with 70 kilojoules.”  (A joule is about 4.2 calories, if you’re wondering.)

Wikipedia, drawing from articles published in *The Journal of Nutrition* and on PubMed, provides a bit more information:

  • Carbohydrates: 5 to 15% of the energy consumed
  • Protein: 20 to 35%
  • Fats: at most 5 to 15 %

Based on this, a negative calorie outcome seems unlikely.  To illustrate, let’s turn to the list of “zero calorie foods” that got me interested.  It consists of Apple, Apricot, Asparagus, Aubergine, Beetroot, Blackberries, Blueberries, Broccoli, Butternut Squash, Cabbage, Cantaloupe, Carrot, Cauliflower, Celery, Chili Peppers, Cranberries, Cress, Cucumber, Endive, Garlic, Grapefruit, Green Bean, Green Tea, Honeydew Melon, Kelp, Lemon, Lettuce, Lime, Mango, Mushrooms, Onion, Papaya, Peach, Pineapple, Radish, Raspberries, Spinach, Strawberries, Tangerine, Tomato, Turnip, Watermelon, and Zucchini.  Of these, the FDA’s Nutrition Information for Raw Fruits, Vegetables, and Fish provided calorie information for the following:

  • Apple, 16.25 kcal/ounce
  • Asparagus, 6.06 kcal/ounce
  • Broccoli, 8.49 kcal/ounce
  • Cantaloupe, 10.42 kcal/ounce
  • Carrot, 10.74 kcal/ounce
  • Cauliflower, 7.14 kcal/ounce
  • Celery, 6.41 kcal/ounce
  • Cucumber, 2.86 kcal/ounce
  • Grapefruit, 10.91 kcal/ounce
  • Green Bean, 6.66 kcal/ounce
  • Honeydew Melon, 10.42 kcal/ounce
  • Lemon, 7.14 kcal/ounce
  • Lettuce, 5 kcal/ounce
  • Lime, 8.33 kcal/ounce
  • Mushrooms, 6.66 kcal/ounce
  • Onion, 15 kcal/ounce
  • Peach, 11.32 kcal/ounce
  • Pineapple, 12.5 kcal/ounce
  • Radish, 3.33 kcal/ounce
  • Strawberries, 9.43 kcal/ounce
  • Tangerine, 12.82 kcal/ounce
  • Tomato, 4.72 kcal/ounce
  • Watermelon, 8 kcal/ounce

That’s quite a range, isn’t it?  2.86 kcal/ounce at the low end and 16.25 kcal/ounce at the high end, with no real explanation given of how these foods are selected or why other foods with a calorie content of 16.25 kcal/ounce or less are excluded.  For comparison purposes, here’s some meat (according to the USDA):

  • Roasted Chicken Breast, 56.66 kcal/ounce
  • Roasted Turkey Breast, 53.33 kcal/ounce
  • Broiled Pork Loin Chop, 60 kcal/ounce
  • Roasted Round Eye Round Stake, 56.66 kcal/ounce

Obviously, plants have less concentrated calories per ounce than meat.  However, it doesn’t appear from the evidence that “zero calorie foods” are a thing, or that it’s worth the time and energy to chase them – using the worst case numbers, you’d keep about 85% of the energy in an ounce of apple (largely carbohydrates) and 70% of the energy in a steak (largely protein), or about 13.81 kcal/ounce for the apple and 39.66 kcal/ounce for the steak.  Heck, you keep 5.45 kcal/ounce of the energy from celery, and that’s the stereotypical diet food.  It makes more sense to me to pursue a balanced diet, composed more of vegetables and fruit than meat.

Ultimately, losing weight requires exercise and reasonable food choices and eating fewer calories than you burn.  Fruits and vegetables, with their lower calorie to bulk ratio, help with this – you can eat more and feel full for fewer calories.  As a bonus, they also tend to be loaded up with vitamins.  But there’s no magic pill that makes the pounds melt off, no one strange trick to shed weight.  In health and nutrition, just like in the financial world. there ain’t no such thing as a free lunch.

Calories Burned:  3,697
Calories Consumed:  2,050
Distance Walked:  2.10 miles (missed my goal but, in fairness, I spent the day with a son with an ear infection…)


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