This is often referred to as the "definitive study"on coconut oil and hair protein loss. However, it is not said in the study, as is often stated on the Internet, that the observed protein loss coconut oil can prevent is from inside the hair shaft. An explanation is given as to why in detail. The hair tested was washed with sodium laureth sulfate only, not shampoo, after initially being cleaned, See Pages 178, 179 and 180. Most commercial shampoos today contain one or more quaternary ammonium compounds, e.g. polyquaternium 10, which also acts as a combing aid.
This text below is quoted directly from the study, on Pages 185 and 186, colour added by me. See Page 180, which names the protein loss testing method used.
"RESULTS AND DISCUSSION
The process of cuticle chipping that results from abrasion of hair against objects such as grooming devices or even other hair is a major factor in hair damage. The proteins that constitute the cuticle cells are lost during wet combing. It is well known that wet combing is accompanied by the breaking of the surface cuticle cell because of its brittleness. Histologically, the major component of the cuticle cell consists of the exocuticle and the endocuticle. The exocuticle, being highly cross-linked is not swollen by water. The endocuticle and the cell membrane complex, on the other hand, are less cross-linked and are more vulnerable to swelling damage. This leads to the lifting of the surface cuticle via bending. Such cuticle cells can be broken in the process of combing or teasing. The protein loss observed in these measurements results mostly from the cuticular region. Because of the short time involved in the combing and brief immersion of the combed tress in water, it is unlikely that proteins from the bulk of the fiber are involved in this measurement."
In the first study undertaken by the same company, a commercial shampoo used (shampoo 1), showed almost the same results on curly and straight hair as the use of coconut oil as a "prewash treatment", See the graphs on Page 334. The text on the left underneath the graph "Figure 6.", should have said without coconut oil. See this blog post on pre-wash treatments.
After rereading their 2001 study on coconut oil hair penetration, hygral fatique and mineral oil, it supports what I wrote in the post below and in this one, plus research in this blog post and the 2012 COSSMA reference here.
The researchers submerged untreated and oil-treated hair in water for one hour, See Page 182 and quoted from Pages 183 and 184, colour added by me.
"While both oil-treated categories show a significant decrease in swelling, it is slightly greater for the coconut-oil-treated fibers than the mineral-oil treated specimens. In coconut-and mineral-oil-treated specimens, swelling is reduced by 48% and 33%, respectively. This strongly suggests that the fiber is protected from damage by hygral fatigue (swelling and de-swelling).
It should be emphasized that the reduction in moisturization of the fiber does not make the fiber rigid because of the plasticizating action of the absorbed coconut oil. ...
Mineral oil also shows lower levels of swelling compared to the untreated fiber, suggesting that it may have penetrated into the cuticular regions, thereby preventing further penetration of water into the hair shaft during the swelling experiment.
Significant reduction in swelling suggests that this will prevent swelling and deswelling (hygral fatigue) of the fiber. Hygral fatigue can lead to cuticular damage as well as damage to the cortex, which can, in turn, affect the mechanical properties."
In other words, mineral oil can also reduce too much water from entering the hair shaft and it can penetrate deeper than just the surface of the hair. Coconut oil in experiments on hair without barrier coatings does not make hair stiff when it penetrates hair, See Pages 170 and 171 for information on the hair used and how it was prepared just before the testing for oil penetration (washed with sodium laureth sulfate).
From results reported on oil shampoo and my own results with it, lauric acid penetration and penetration to a lesser degree by the other fatty acids in coconut oil did not result in stiff or "crunchy" (very dry) hair either, even when coconut oil was used over a period of time. I have read numerous reports online of coconut oil use causing hair to become "hard" feeling and dry.
This blog post for more details