I've been reading about bulletproof coffee lately and it made me wonder what the benefits were of having nothing but fat as a "breakfast" in the morning. I didn't see any previous questions about this so forgive me if I've asked a question that has already been answered. Does anyone have any thoughts or personal experiences on this?
A high-fat/low-carb breakfast (a la "bulletproof" coffee) will likely affect the body in ways similar to fasting. To see how this works, we can look at the following graph which tracks the respiratory quotient of individuals under different circumstances and metabolic inclinations.
In the upper left hand corner of the graph, you can see the shift in metabolism from "glycolytic" (ie. sugar burning) to oxidative (ie. fat burning) over the course of an overnight fast. The black dotted line shows a "metabolically flexible" person (the term refers to the capacity to match metabolic processes to the available fuel source) while the white dotted line shows a metabolically "inflexible" person (typical of obese or T2 diabetics).
You can see how the overnight fast in the upper left hand corner is similar to the high fat diet in the lower right corner.
Conversely, you can see how a high carbohydrate diet is similar to an "insulin clamp" (a simultaneous infusion of both glucose and insulin).
This shows that the metabolically flexible person is both better at burning glucose and burning fat than the metabolically inflexible person. The underlying causes of metabolic flexibility/inflexibility are likely related to numerous factors, but it seems at least theoretically possible that you would enhance metabolic flexibility by challenging the body to switch from one fuel source to another.
Any regimen where you prolong fat metabolism (by fasting completely or eating only fat for breakfast) and only intermittently spike insulin release/glucose may accomplish this.
Benefits of Fat:
I'm not generally hungry before leaving the house in the morning, so Bulletproof coffee is my go-to. It keeps me satisfied until around 4 in the afternoon. I use a 32-oz French press with 1.5 Tbs coffee, 3 Tbs MCT oil, and 3 Tbs unsalted Kerrygold.
I only drink it on my early mornings and just eat when I'm hungry the other days.
Coffee doesn't usually sit well with me either (after sending me rushing to the bathroom, I come out feeling very hungry), but on mornings that I don't have much appetite, blueberries with canned coconut milk feels pretty great. It's the only low-protein breakfast I've found so far that agrees with my metabolism.
^ That is my favorite way to start the day.
EDIT: To answer your question though, the benefits of starting the day off with fat are
It helps sell bullet-proof coffee.
It makes you feel guilt-free when putting a knob of butter into your coffee.
Real fasting occurs when you do not experience physiologic taste satisfaction and your body uses endogenous fat stores (not exogenous fat consumption) for energy.
I love starting the day off with a nice cup of Joe and 3 heaping tablespoons of coconut oil. It keeps me satiated and gives me tons of energy. Eating too early doesn't sound to appetizing anyway.
Coffee doesn't make my stomach happy, but I still go with fat for breakfast and find it keeps me satisfied longer. I will either eat 1/2 - 1 whole avocado with a pinch of salt and pepper or a few teaspoons of coconut manna.
My husband and I love our bulletproof coffee! We both feel fantastic after drinking it. No hunger and lots of energy. I drink it and eat about 4-6 hours later, but my husband can go 7-8 hours before eating. We don't always wait that long, but it is satisfying. I kinda have to nurse it sometimes because it is so heavy. The later I finish it the later I eat.
I feel much more satisfied after bulletproof coffee than most other things. The only other thing that satisfies me a similar amount of time (about 3-4 hours) is eggs and pemmican or eggs and sausage. I know that is not fat only, but just saying bulletproof coffee actually lasts longer than a protein source for me.
Some of the benefits of a fat only breakfast are also thanks to the lack of protein as well as lack of carbs. Some of the benefits of fasting come from an extended window with no protein; it prompts the so-called autophagy (basically forces our cells to clean house for a bit). That where one would argue a lot of the cancer detering affect of interimitten fasting comes from. Just like an IF, a fat only breakfast doesn't interup either the nice overnight insulin drop into fatburning, nor the cellular cleanup process... until a late lunch Bacon salad of course! :).