user8157: In the Puttamansa Sutta, the Four Nutriments ('ahara') of physical food, sense contact, intention & consciousness are discussed using four comparative similes ('metaphors'). 
The 1st simile of eating the flesh of one's own son (merely for the sake of crossing the desert) is very straightforward. However, the remaining three similes of a 'skinned cow', of 'two strong men dragging a man into a pit of fire' & of a 'thief punished by a king' are not obvious in their meaning. 
These three similes are: 

And how, O monks, should the nutriment sense-impression be considered? Suppose, O monks, there is a skinned cow that stands close
  to a wall, then the creatures living in the wall will nibble at the
  cow; and if the skinned cow stands near a tree, then the creatures
  living in the tree will nibble at it; if it stands in the water, the
  creatures living in the water will nibble at it; if it stands in the
  open air, the creatures living in the air will nibble at it. Wherever
  that skinned cow stands, the creatures living there will nibble at
  it.
And how, O monks, should the nutriment volitional thought be considered? Suppose, O monks, there is a pit of glowing embers, filled
  to cover a man's height, with embers glowing without flames and smoke.
  Now a man comes that way, who loves life and does not wish to die, who
  wishes for happiness and detests suffering. Then two strong men would
  seize both his arms and drag him to the pit of glowing embers. Then, O
  monks, far away from it would recoil that man's will, far away from it
  his longing, far away his inclination. And why? Because the man knows:
  'If I fall into that pit of glowing embers, I shall meet death or
  deadly pain.'
And how, O monks, should the nutriment consciousness be considered? Suppose, O monks, people have seized a criminal, a robber, and brought
  him before the king saying: 'This is a criminal, a robber, O Majesty!
  Mete out to him the punishment you think fit!' Then the king would
  tell them: 'Go, and in the morning strike this man with a hundred
  spears!' And they strike him in the morning with a hundred spears. At
  noon the king would ask his men: 'How is that man?' — 'He is still
  alive, Your Majesty.' — 'Then go and strike him again at noontime with
  a hundred spears!' So they did, and in the evening the king asks them
  again: 'How is that man?' — 'He is still alive.' — 'Then go and in the
  evening strike him again with a hundred spears!' And so they did.

What do we think each of these similes means? 

user8044: Existence is nourished by four nutriments as pointed out in the Sutta in @Dhammadhatu ‘s OP. They are essential to continue life in this repeated existence in samsara. This is true even to the deities in the celestial world and brahmas in the Brahma world. Of these four kinds, one is material/physical, and the other three are mental nutriments. The first is the easy one as @Dhammadhatu pointed out. But how can one see one’s mental state or mental growth if not for the guidance that the Buddha provided in many of the suttas? The Buddha provided the explanation in the Atthi Raga Sutta (where there is passion) in the Samyutta Nikaya.
How we have to view the four similes is that ONLY if we eradicate the Cause, would the Result be eradicated, and NOT otherwise. It is our Desire for Life that prevents this. The day that we establish wisdom over ignorance, and liberation over desire, we will see the light. The day we remove our passion, delight and craving for the four nutriments Consciousness will not arise. Then mentality-materiality won’t happen, and as a result there is no growth of fabrications, and no renewed becoming. If no future birth, there is no decay, death, sorrow, lamentation, pain, grief and despair.
To explain the 2nd simile -  that of the nutriment sense-impression:
Sense impression (phassa ahara) is Contact.  So what is contact? It is the coming together of three things. It is the eye, the visible object and consciousness coming in contact with each other (seeing forms). It is the ear, sounds and consciousness coming in contact with each other (hearing sound). it is the nose, odours and consciousness coming in contact with each other (smelling odours), and likewise. What is important to understand is with the arising of consciousness, it is inevitable for contact to arise. Only if we eradicate the desire for what we see, hear, smell, taste, touch and think, will the contact and consciousness not arise. The simile of the flayed cow is about this contact that one cannot get away from as long as there is desire.
To explain the 3rd simile -  that of the nutriment volitional thought:
Volitional thought (Cetana) is Intellectual Intention. It is the arising of wholesome or unwholesome intentions. As before, these mental factors are a result of desire. Beings who cannot comprehend that these mental factors are not permanent, that they constantly change, and be mindful, gets thrown into the pit whether they like it or not. Only getaway is eradicating the cause – the arising of ‘cetana’ – of intellectual intention.
To explain the 4th simile -  that of the nutriment of Consciousness:
 Our sense faculties are constantly contacted and stimulated because of Consciousness as explained before. The two that I did not touch on are that of the body and intellect.  Dependent on the body and tactile sensations, arises consciousness at the body.  Dependent on the intellect (ideas/thoughts), there arises consciousness at the intellect. With the Consciousness, desire arises. This arising of passion, delight and craving results in greed, hatred and delusion – these are the spears that one gets shot at with. As long as you have passion, delight and craving, you are alive and get shot at and experiences pain and distress.
So our Desire for the Dhamma, to live in the Dhamma should be even greater than our desire for Life. Those are the ones who will stay in the finger tip. What the Buddha has said is patisotagami or against the current of conventional thinking. Buddha knew this well. That is why He said, 

“Dear Bhikkhus, ones who would not realize this Dhamma is like this earth (in amount). Ones who realize this is like this small amount of soil on my finger nail.”


user19155: Its simple, i will explain each 4 nutriement in points
(1) physical food- it is to be regarded only for survival ,not for flavour or intoxication.  We should treat our physical food like we are feeding on our young baby 
(2) contact- if contact happens with our six senses (eye, ear,  skin ,etc) to its corresponding object (vision, touch etc)  then that object chew on it.. for  example if you have eye and lets say its corresponding object is pornography.. then we should regard pornography as something chewing our eye.. ultimately destroying it...but since we normally dont question our sense-object , we enjoy it till our ruin.
(3) volition- buddha said you should regard volition as survival instinct only.... here a man hates death.. but a practitioner sholuld not fear death... so he is saying normally we have volition that act upon survival instinct..we dont act truly but act according to survival instinct 
(4) consciousness- well , if u are ever depressed, tensed and wanted to end your life ,,you should know its all because of your damn consciousness...so consciousness is spear acting upon us..buddha is saying to take this consciousness in command 
Finally,  what he meant is that the above 4 food is necessary for survival. . If you cant survive then how will you attain nirvana...but he is saying dont take these food unmindfully..see what game is undergoing behind the scene..in 1 word right view ...right view about these food is necessary for salvation ..hope it helps. If any question please ask. Glory to Buddha

user2282: While the sutta did not state the nutriments are evil, it did give vivid and explicit similes of the son's flesh, the skinned cow, the man being dragged toward a burning pit, and a criminal being pierced with three hundred spears. Needless to say, one doesn't have to be very smart to think carefully before indulging oneself with the nutriments after hearing what the Buddha just said. Imho, SN 12.63 reflects the Dukkha inherent in all conditioned phenomena. And the Four Nutriments are no exception. For us regular worldlings, we tend to only understand the 1st of the 3 aspects of Dukkha, Dukkha-dukkha, for the obvious reason that it's right there in front of our naked eye. That's why we continue to indulge in the nutriments and sense pleasures. It would take a significant degree of cultivation and penetrative insight to understand the other 2: Viparinama-dukkha and Sankhara-dukkha. And until then, we'd still only be able to have some superficial understanding of what SN 12.63 was trying to say. Per ChrisW's suggestion, I've reposted as an answer and include the 2 very helpful links from Prof. Tan and Ven. Nyanaponika with detailed commentary on SN 12.63:
http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/20.6-Puttamamsa-S-s12.63-piya.pdf
http://www.accesstoinsight.org/lib/authors/nyanaponika/wheel105.html

user8044: The Four Nutriments ('ahara') of physical food, sense contact, intention & consciousness are true for the worldlings who have craving (tanha) and greed (lobha) or aversion / revulsion (dosa), caused by ignorance (moha).  Tanha, lobha, dosa, moha provides nourishment for the continuation of life from existence to existence. 
The worldlings have  five aggregates of clinging (Panca Upadana Khandas).  In the case of Arahants – the awakened ones - there is no craving. They have rooted out the “I concept”.  They have fully realized five groups of existence and the five grasping groups of existence (Panncakkhandha and panca upadanakkhandha) .  Arahants have only the five aggregates in detachment  (Anupadana).  Upadana means ‘grasping’ and Anupadana means ‘non-grasping’ or letting go.While Upadana leads to Samsara, Anupadana leads to Nibbana.
To put it in another way, (for better understanding), after the elimination of all defilements an arahant lives in society without Upadana or Attachment to any thing in the world. He does not have the five grasping groups (pancaupadanakkhandha) but only five groups,aggregates (Pancakkhandha), namely, rupa (body), vedana (feeling), sanna (perception), sankhara (volitional formation), and vinnana (consciousness).  His consciousness is ‘translucent’ (for wont of a better word) as no food is provided. In this he is immeasurable - is like the Buddha. All measurement is from a here to a there, with in-betweens. In the Buddha, there is neither a here nor a there nor any in-between. He is thus immeasurable. See Bahiya Sutta: About Bahiya - Ud 1.10

“Then, Bahiya, you should train yourself thus: In reference to the seen, there will be only the seen. In reference to the heard, only the heard. In reference to the sensed, only the sensed. In reference to the cognized, only the cognized. That is how you should train yourself. When for you there will be only the seen in reference to the seen, only the heard in reference to the heard, only the sensed in reference to the sensed, only the cognized in reference to the cognized, then, Bahiya, there’s no you in that. When there’s no you in that, there’s no you there. When there’s no you there, you are neither here nor yonder nor between the two. This, just this, is the end of stress.” (Ud I.l0)...

An arahant is sustained by ONLY the physical food that does not create upadana. He does not have the other three ‘mental’ foods as he has rooted out the “I concept”.  He is free from attavada upadana by seeing it as a deceit (the true nature). So if there is no nutriment  consciousness, an Arahants  consciousness is mere presence.  Since there cannot be presence without something being present, it is what distinguishes living from non-living, such as tables and chairs. The Buddha has stated that consciousness is dependently arisen, since without a condition there is no origination of consciousness. In an Arahant, Paticcasamuppada (dependent arising) ceases.  Which means Vinnana paccaya (conditioned by consciousness) too ceases.

8157: <p>In the <a href="http://www.accesstoinsight.org/tipitaka/sn/sn12/sn12.063.nypo.html" rel="nofollow">Puttamansa Sutta</a>, the Four Nutriments ('ahara') of physical food, sense contact, intention &amp; consciousness are discussed using four comparative similes ('metaphors'). </p>

<p>The 1st simile of eating the flesh of one's own son (merely for the sake of crossing the desert) is very straightforward. However, the remaining three similes of a '<em>skinned cow</em>', of '<em>two strong men dragging a man into a pit of fire</em>' &amp; of a '<em>thief punished by a king</em>' are not obvious in their meaning. </p>

<p>These three similes are: </p>

<blockquote>
  <p><em>And how, O monks, should the nutriment <strong>sense-impression</strong> be considered? Suppose, O monks, there is a skinned cow that stands close
  to a wall, then the creatures living in the wall will nibble at the
  cow; and if the skinned cow stands near a tree, then the creatures
  living in the tree will nibble at it; if it stands in the water, the
  creatures living in the water will nibble at it; if it stands in the
  open air, the creatures living in the air will nibble at it. Wherever
  that skinned cow stands, the creatures living there will nibble at
  it.</em></p>
  
  <p><em>And how, O monks, should the nutriment <strong>volitional thought</strong> be considered? Suppose, O monks, there is a pit of glowing embers, filled
  to cover a man's height, with embers glowing without flames and smoke.
  Now a man comes that way, who loves life and does not wish to die, who
  wishes for happiness and detests suffering. Then two strong men would
  seize both his arms and drag him to the pit of glowing embers. Then, O
  monks, far away from it would recoil that man's will, far away from it
  his longing, far away his inclination. And why? Because the man knows:
  'If I fall into that pit of glowing embers, I shall meet death or
  deadly pain.</em>'</p>
  
  <p><em>And how, O monks, should the nutriment <strong>consciousness</strong> be considered? Suppose, O monks, people have seized a criminal, a robber, and brought
  him before the king saying: 'This is a criminal, a robber, O Majesty!
  Mete out to him the punishment you think fit!' Then the king would
  tell them: 'Go, and in the morning strike this man with a hundred
  spears!' And they strike him in the morning with a hundred spears. At
  noon the king would ask his men: 'How is that man?' — 'He is still
  alive, Your Majesty.' — 'Then go and strike him again at noontime with
  a hundred spears!' So they did, and in the evening the king asks them
  again: 'How is that man?' — 'He is still alive.' — 'Then go and in the
  evening strike him again with a hundred spears!' And so they did.</em></p>
</blockquote>

<p>What do we think each of these similes means? </p>
 8044: <p>Existence is nourished by four nutriments as pointed out in the Sutta in @Dhammadhatu ‘s OP. They are essential to continue life in this repeated existence in samsara. This is true even to the deities in the celestial world and brahmas in the Brahma world. Of these four kinds, one is material/physical, and the other three are mental nutriments. The first is the easy one as @Dhammadhatu pointed out. But how can one see one’s mental state or mental growth if not for the guidance that the Buddha provided in many of the suttas? The Buddha provided the explanation in the <a href="http://www.accesstoinsight.org/tipitaka/sn/sn12/sn12.064.than.html" rel="nofollow">Atthi Raga Sutta (where there is passion) in the Samyutta Nikaya</a>.</p>

<p>How we have to view the four similes is that ONLY if we eradicate the Cause, would the Result be eradicated, and NOT otherwise. It is our Desire for Life that prevents this. The day that we establish wisdom over ignorance, and liberation over desire, we will see the light. The day we remove our passion, delight and craving for the four nutriments Consciousness will not arise. Then mentality-materiality won’t happen, and as a result there is no growth of fabrications, and no renewed becoming. If no future birth, there is no decay, death, sorrow, lamentation, pain, grief and despair.</p>

<p><strong>To explain the 2nd simile -  that of the nutriment sense-impression:</strong><br>
Sense impression (phassa ahara) is Contact.  So what is contact? It is the coming together of three things. It is the eye, the visible object and consciousness coming in contact with each other (seeing forms). It is the ear, sounds and consciousness coming in contact with each other (hearing sound). it is the nose, odours and consciousness coming in contact with each other (smelling odours), and likewise. What is important to understand is with the arising of consciousness, it is inevitable for contact to arise. Only if we eradicate the desire for what we see, hear, smell, taste, touch and think, will the contact and consciousness not arise. The simile of the flayed cow is about this contact that one cannot get away from as long as there is desire.</p>

<p><strong>To explain the 3rd simile -  that of the nutriment volitional thought:</strong><br>
Volitional thought (Cetana) is Intellectual Intention. It is the arising of wholesome or unwholesome intentions. As before, these mental factors are a result of desire. Beings who cannot comprehend that these mental factors are not permanent, that they constantly change, and be mindful, gets thrown into the pit whether they like it or not. Only getaway is eradicating the cause – the arising of ‘cetana’ – of intellectual intention.</p>

<p><strong>To explain the 4th simile -  that of the nutriment of Consciousness:</strong><br>
 Our sense faculties are constantly contacted and stimulated because of Consciousness as explained before. The two that I did not touch on are that of the body and intellect.  Dependent on the body and tactile sensations, arises consciousness at the body.  Dependent on the intellect (ideas/thoughts), there arises consciousness at the intellect. With the Consciousness, desire arises. This arising of passion, delight and craving results in greed, hatred and delusion – these are the spears that one gets shot at with. As long as you have passion, delight and craving, you are alive and get shot at and experiences pain and distress.</p>

<p>So our Desire for the Dhamma, to live in the Dhamma should be even greater than our desire for Life. Those are the ones who will stay in the finger tip. What the Buddha has said is patisotagami or against the current of conventional thinking. Buddha knew this well. That is why He said, </p>

<blockquote>
  <p>“Dear Bhikkhus, ones who would not realize this Dhamma is like this earth (in amount). Ones who realize this is like this small amount of soil on my finger nail.”</p>
</blockquote>
 19155: <p>Its simple, i will explain each 4 nutriement in points</p>

<p>(1) physical food- it is to be regarded only for survival ,not for flavour or intoxication.  We should treat our physical food like we are feeding on our young baby </p>

<p>(2) contact- if contact happens with our six senses (eye, ear,  skin ,etc) to its corresponding object (vision, touch etc)  then that object chew on it.. for  example if you have eye and lets say its corresponding object is pornography.. then we should regard pornography as something chewing our eye.. ultimately destroying it...but since we normally dont question our sense-object , we enjoy it till our ruin.</p>

<p>(3) volition- buddha said you should regard volition as survival instinct only.... here a man hates death.. but a practitioner sholuld not fear death... so he is saying normally we have volition that act upon survival instinct..we dont act truly but act according to survival instinct </p>

<p>(4) consciousness- well , if u are ever depressed, tensed and wanted to end your life ,,you should know its all because of your damn consciousness...so consciousness is spear acting upon us..buddha is saying to take this consciousness in command </p>

<p>Finally,  what he meant is that the above 4 food is necessary for survival. . If you cant survive then how will you attain nirvana...but he is saying dont take these food unmindfully..see what game is undergoing behind the scene..in 1 word right view ...right view about these food is necessary for salvation ..hope it helps. If any question please ask. Glory to Buddha</p>
 2282: <p>While the sutta did not state the nutriments are evil, it did give vivid and explicit similes of the son's flesh, the skinned cow, the man being dragged toward a burning pit, and a criminal being pierced with three hundred spears. Needless to say, one doesn't have to be very smart to think carefully before indulging oneself with the nutriments after hearing what the Buddha just said. Imho, SN 12.63 reflects the Dukkha inherent in all conditioned phenomena. And the Four Nutriments are no exception. For us regular worldlings, we tend to only understand the 1st of the 3 aspects of Dukkha, Dukkha-dukkha, for the obvious reason that it's right there in front of our naked eye. That's why we continue to indulge in the nutriments and sense pleasures. It would take a significant degree of cultivation and penetrative insight to understand the other 2: Viparinama-dukkha and Sankhara-dukkha. And until then, we'd still only be able to have some superficial understanding of what SN 12.63 was trying to say. Per ChrisW's suggestion, I've reposted as an answer and include the 2 very helpful links from Prof. Tan and Ven. Nyanaponika with detailed commentary on SN 12.63:<br/>
<a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/20.6-Puttamamsa-S-s12.63-piya.pdf" rel="nofollow noreferrer">http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/20.6-Puttamamsa-S-s12.63-piya.pdf</a><br/>
<a href="http://www.accesstoinsight.org/lib/authors/nyanaponika/wheel105.html" rel="nofollow noreferrer">http://www.accesstoinsight.org/lib/authors/nyanaponika/wheel105.html</a></p>
 8044: <p>The Four Nutriments ('ahara') of physical food, sense contact, intention &amp; consciousness are true for the worldlings who have craving (tanha) and greed (lobha) or aversion / revulsion (dosa), caused by ignorance (moha).  Tanha, lobha, dosa, moha provides nourishment for the continuation of life from existence to existence. </p>

<p>The worldlings have  five aggregates of clinging (Panca Upadana Khandas).  In the case of Arahants – the awakened ones - there is no craving. They have rooted out the “I concept”.  They have fully realized five groups of existence and the five grasping groups of existence (Panncakkhandha and panca upadanakkhandha) .  Arahants have only the five aggregates in detachment  (Anupadana).  Upadana means ‘grasping’ and Anupadana means ‘non-grasping’ or letting go.While Upadana leads to Samsara, Anupadana leads to Nibbana.</p>

<p>To put it in another way, (for better understanding), after the elimination of all defilements an arahant lives in society without Upadana or Attachment to any thing in the world. He does not have the five grasping groups (pancaupadanakkhandha) but only five groups,aggregates (Pancakkhandha), namely, rupa (body), vedana (feeling), sanna (perception), sankhara (volitional formation), and vinnana (consciousness).  His consciousness is ‘translucent’ (for wont of a better word) as no food is provided. In this he is immeasurable - is like the Buddha. All measurement is from a here to a there, with in-betweens. In the Buddha, there is neither a here nor a there nor any in-between. He is thus immeasurable. See <a href="http://www.accesstoinsight.org/tipitaka/kn/ud/ud.1.10.irel.html" rel="nofollow">Bahiya Sutta: About Bahiya - Ud 1.10</a></p>

<blockquote>
  <p>“Then, Bahiya, you should train yourself thus: In reference to the seen, there will be only the seen. In reference to the heard, only the heard. In reference to the sensed, only the sensed. In reference to the cognized, only the cognized. That is how you should train yourself. When for you there will be only the seen in reference to the seen, only the heard in reference to the heard, only the sensed in reference to the sensed, only the cognized in reference to the cognized, then, Bahiya, there’s no you in that. When there’s no you in that, there’s no you there. When there’s no you there, you are neither here nor yonder nor between the two. This, just this, is the end of stress.” (Ud I.l0)...</p>
</blockquote>

<p>An arahant is sustained by ONLY the physical food that does not create upadana. He does not have the other three ‘mental’ foods as he has rooted out the “I concept”.  He is free from attavada upadana by seeing it as a deceit (the true nature). So if there is no nutriment  consciousness, an Arahants  consciousness is mere presence.  Since there cannot be presence without something being present, it is what distinguishes living from non-living, such as tables and chairs. The Buddha has stated that consciousness is dependently arisen, since without a condition there is no origination of consciousness. In an Arahant, Paticcasamuppada (dependent arising) ceases.  Which means Vinnana paccaya (conditioned by consciousness) too ceases.</p>
