For the accomplishment of knowledge and insight it is necessary to be energetic.
Right on up to the point of achieving Arahantship there will be an energy-consuming effort to end bad habits that are present in one, prevent bad habits that are not yet present, acquire good habits that are not yet present and retain good habits that are present.
Even the jhānas, which in theory require less energy than sleep, will require an enormous struggle with bad habits of body and mind before any lasting success at entering and maintaining them can be expected.
Energy is not acquired by eating more energy-producing food.
Energy is acquired by the expenditure of energy in ending bad energy-wasting habits that are present in one, preventing bad energy-wasting habits that are not yet present, acquiring good energy-conserving habits that are not yet present and retaining good energy-conserving habits that are present.
This is a way of saying that what is required is a re-organization of one's energy allocations ... by the way, one of Don Juan's most important teachings.
Two areas where energy is commonly mis-deployed and can be usefully re-allocated are food consumption and sleep.
If you notice you are putting on weight in the form of fat, you are eating more than your body needs to produce the energy required to accomplish what needs to be accomplished by the body during the day: you are wasting energy.
Energy is being wasted on the expense of the wasted food.
Energy is being expended in the digestion of the surplus food.
Energy is being expended in the storage and management of the extra nutrients (fat).
The body is expending extra energy in carrying around the extra weight.
Consuming more food than the body needs to produce the energy required to accomplish what needs to be accomplished by the body during the day results in fatigue.
Feeling fatigue one sleeps or dozes or passes time in a daze. This is not helpful in attaining knowledge and insight.
Sleep, beyond what the body needs to restore the alertness of the mind to accomplish what needs to be accomplished by the body during the day is a waste of valuable time that could be used for ending bad habits that are present in one, preventing bad habits that are not yet present, acquiring good habits that are not yet present and retaining good habits that are present.
At the onset of fatigue, before stored energy is used, the body indicates a need for extra energy in the form of desire to eat. Acting on that desire is the fueling of the activities of the body that result from consuming more food than your body needs to produce the energy required to accomplish what needs to be accomplished by the body during the day, and not only does not consume previously stored nutrients, but adds to the storage burden.
Noticing the burden (you see you are getting fat) and resorting to exercise is the addition of extra energy consuming activity to the daily routine, results in additional demands for nutrients to support that new activity which creates a completely useless energy-consuming cycle and does nothing to add to the energy supply or time needed to develop knowledge and insight.
If unnecessary exercise does result in a healthy-appearing body, it will also result in the need to maintain that level of activity (and thereby reduce by that much time over time the time one could be using to develop knowledge and insight) and the result of that will be a habit of consumption of food based on that higher level of activity and should there come a time when that exercise is no longer possible or desirable, the consequence will be energy-consuming and mentally disturbing fatty flab.
To bring the consumption of food down to the non-useless-exercise level is the same task as would be required to cut down on the original level of over-consumption that resulted in the overweight that resulted in the exercise in the first place.
Consumption of energy stimulants (herbs, pills, powders, caffeinated drinks) work by combining a draw-down on emergency energy supplies (by stimulating adrenalin production) and the suppression of the appetite that results in consuming more food than your body needs to produce the energy required to accomplish what needs to be accomplished by the body during the day and the result of that in fatigue.
This is the left hand stealing from the right hand.
What goes up must come down.
If this artificial energy boost is used productively, the knowledge and insight gained will be that the habit of using energy stimulants is a hindrance to further knowledge and insight and will need to be eliminated. Back to square one.
We say nothing here about the danger to the quest for knowledge and insight that the danger that extra weight poses to the health of the body creates, including the time, energy and expense (and the time and energy expended in acquiring the funds to meet those expenses) consumed in battling disease caused by being overweight and of slothful habits.
Part of knowledge and insight is recognizing where we are behaving like a fool and eliminating those behaviors.