In the Light of Egypt, first published in 1889 and referenced in this previous post, Thomas Burgoyne makes the following statement while examining the connection between the spiritual and material worlds: 
Ask Science how the plant grows, what causes the atoms of matter to build up root, stem, leaf, bud and flower, true to the parent species from which the germinal atom came.  What is there behind the plant that stamps it with such striking individuality?  And why, from the same soil, the deadly aconite and nutritious vegetable can grow, each producing qualities in harmony with its own nature, so widely different in their effects upon the human organism, yet, so completely identical as regards the source from which they appear to springvolume 2, page 58.
He then goes on to quote the work of Scottish agricultural chemist James Finlay Weir Johnson (1796 - 1855), who in his Chemistry of Common Life wrote:
How interesting it is to reflect on the minuteness of the organs by which the largest plants are fed and sustained.  Microscopic apertures in the leaf suck in gaseous food from the air; the surfaces of microscopic hairs suck a liquid food from the soil.  We are accustomed to admire, with natural and just astonishment, how huge, rocky reefs, hundreds of miles in length, can be built up by the conjoined labors of myriads of minute zoophytes, laboring together on the surface of a coral rock; but it is not less wonderful that, by the ceaseless working of similar microscopic agencies in leaf and root, the substance of vast forests should be built up and made to grow before our eyes.  It is more wonderful, in fact; for whereas, in the one case, the chief result is that dead matter extracted from the sea is transformed into a dead rock; in the other, the lifeless matter of the earth and air are converted by these minute plant-builders into living forms, lifting their heads aloft to the sky, waving with every wind that blows, and beautifying whole continents with the varying verdure of their ever-changing leaves.  59.
This is remarkable to consider -- where, for instance, does the mighty sequoia draw the matter that turns it from a tiny seed into an enormous tree, the largest tree by volume on earth?  All that matter was somehow transmuted from soil into living plant, tens of thousands of cubic feet in volume.  

We can readily see why Thomas Burgoyne chose to ask his readers to ponder this mystery as he explores the connection between the material and the spiritual.  Pointing out that the same soil can be transmuted into two different plants of very different characteristics -- that the same soil can, in fact, produce a plant of deadly poison and right next to it a plant bearing nourishing vegetables -- he asserts that the plant is expressing in the material plane a spiritual reality, the force which rearranges the inorganic molecules drawn from the soil into the organic molecules of the tree:
We know that the plant, being the physical expression upon the material plane of a more interior life, endows its outward atoms with their peculiar qualities.  These qualities are not drawn directly from the soil; the soil only becoming the medium for their complete or incomplete expression, as the case may be; i.e., supplying the necessary inorganic atoms.   Hence, the deadly qualities of aconite, and the generous life-sustaining qualities of the nutritious vegetable, being spiritual life-endowments, conveyed to the material substance, abstracted from the soil and withdrawn from the atmosphere, are no mystery; their effect upon the human organism being exactly that, which is produced by their spiritual affinity or antipathy, as the case may be.  And this also shows and explains, why purely inorganic chemical atoms, though they be exactly the same as the organic substances, from a strictly scientific standpoint, yet fail to support life, because such chemical equivalents lack the organic spirituality of the interior life, which alone gives them the power and function to support the same.  61.
From the above series of assertions, Mr. Burgoyne then makes an interesting application:  
Vegetables, fresh from the ground, or parent stem, retain this life if at once prepared for food, if not overcooked, which is so often ignorantly done.  This is the secret of sustenance from foods.  Nature's perfected fruits and vegetables are overflowing with the life-giving essences, and, if eaten direct from the tree or parent stem, that life is not lost, but transmitted to our organisms, and replenishes the wasting system with a living life.  Much less of such food is required to completely satisfy and nourish the body than if the life had partly departed or been destroyed.  61.
So, these metaphysical reflections on the relationship between the material and spiritual led Mr. Burgoyne to publish an assertion back in the 1800s with which modern "raw foodists" can readily agree.  He cautions us against overcooking, "which is so often ignorantly done," and to strive to consume fresh fruits and vegetables "direct from the tree or parent stem," before they are "too long severed from the medium which transmits the spiritual life."

Widespread awareness of the health benefits of consuming a higher percentage of "raw food" (or even 100% raw food) is a relatively new phenomenon.  Raw food advocates often define "raw" in terms corresponding to this definition found in Going Raw, by Judita Wignall: "Raw food is fresh, whole food that has not been refined, chemically processed, or heated above118o F (48o C), so its nutritional content is preserved" (11).  

The benefits claimed for consuming more plant-based foods in their raw state often include less nutrient loss and less formation of various harmful substances and toxins that can be produced when foods are heated to higher temperatures.  This previous post, for instance, cited evidence that heating certain vegetable oils can cause them to become oxidized or rancid, and to release free radicals that can be harmful to the human body.  Many of the vegetable oils that have become standard in the "modern western diet" since the Second World War (but which were rarely used in cooking prior to that time) fall into this category.

Interestingly, the benefits that raw food advocates usually cite are mainly "material" (as opposed to "spiritual" or "metaphysical"), but  based on the important discussion by Thomas Burgoyne above, we might conclude that the most critical reason to increase the consumption of fresh, uncooked fruits and vegetables in the diet is beyond the purview of traditional science and can be said to be "spiritual" in nature.

While the raw diet may be perceived as "extreme," Judita Wignall points out that one does not have to commit to eating all food raw in order to increase the consumption of fresh uncooked fruits and vegetables:
You don't need to be a vegetarian or vegan to go raw, nor do you need to be 100 percent raw to reap many of the diet's benefits.  Any amount of raw food is beneficial, but try to aim for a 50 percent raw diet to feel a notable difference.  Think about it this way: If you just add a smoothie to your morning routine and a salad before lunch and dinner, you're already there!  21.
This would appear to be yet another area in which long-suppressed ancient knowledge can be seen to have extremely practical and daily application to our lives.