Talk:Lipid: Difference between revisions

Content deleted Content added

Inline

Revision as of 12:53, 14 October 2010

{{ArticleHistory lick my balls | action1link = | action1result = listed | action1oldid = 31753188

| currentstatus = GA | topic = natsci }} Template:WikiProject Molecular and Cellular Biology

This article was reviewed by Nature on December 14, 2005.
Comments: No significant errors or major omissions were identified.
For more information about external reviews of Wikipedia articles and about this review in particular, see this page.

Lipids are fatty acid esters... and cholesterol as lipid

Most of what I have seen counts cholesterol lipids, and this page in fact does so when it lists the hydrophobic and hydrophilic groups, but cholesterol is definitely not a fatty acid ester.

Jedi Dan, Cholesterol molecules are not lipids. They are actually a series of circular hydrocarbon molecules, each bonded together. I cant remember exactly what cholesterol looks like, but cholesterol and the steroid hormones derived from it typically have hydroxyl (OH), ketone/aldehyde (C=O) and methyl groups on them.

What he said is correct, assuming R1' to be a hydrocarbon chain (except the last carbon atom) and R2' to be a glycerol molecule, you could show it to be R1'-CO-O-R2' where the CO is a double bond. Check out the links below, they would probably explain better than I can in text.

Read more about steroid hormones/cholesterol at http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Cholesterol.html

Read more about triglycerides at http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/Fats.html

I too have generally thought cholesterol and steroids as not being "lipids". However, the following passage appears in General Chemistry Online!: "lipid. A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophobic. Examples are fats, oils, waxes, and steroids." Likewise the Drug Discovery & Development Glossary states that a lipid is "an oil-soluble molecule such as a fatty acid or steroid." If on the other hand one looks at the IUPAC Nomenclature Recommendations, lipids and steroids are classed differently. Under IUPAC Nomenclature, lipids are a class of molecules that includes fatty acids, neutral fats, long-chain alcohols, long-chain bases, phospholipids, glycolipids and neuraminic acid. Therefore, I'd say that "lipids include steroids when the term (lipid) is used in a colloquial sense; however, from an organic chemistry nomenclature point of view, steroids are formally excluded from the lipid-class of molecules." Courtland 01:52, 2005 Mar 8 (UTC)
Here's a more concise view which is part of the IUPAC Glossary of Class Names, the Lipid entry, which goes into specifics of what is included in the class: http://www.chem.qmul.ac.uk/iupac/class/lipid.html. Now this page says that the term lipid is "a loosely defined term for substances of biological origin that are soluble in nonpolar solvents. They consist of saponifiable lipids, such as glycerides (fats and oils) and phospholipids, as well as nonsaponifiable lipids, principally steroids." Therefore, steroids are lipids afterall and their separation in the IUPAC nomenclature does not indicate they are unrelated. Courtland 02:03, 2005 Mar 8 (UTC)

Sometimes categories can be incompletely congruent in different contexts. For example, cholesterol is always considered a lipid in a medical context, and this would be a common reason for a reader to look at this article. We need a section on cholesterol and other sterols explaining how they differ from triglycerides and in what contexts they are or are not considered lipids. alteripse 14:07, 24 December 2005 (UTC)[reply]

Cholesterol is a lipid... in all contexts. The problem is that the term lipid refers to a huge variety of hydrophobic biomolecules, which is why things as dissimilar as fatty acids and sterols are classified as lipids. GFP 06:09, 16 June 2006 (UTC)[reply]

More 'What is a lipid?'

Others have noticed that there is no general agreement on the term 'lipid'. W. Christie's review What is a Lipid? is useful. Given that there are so many definitions out there, and that so many of them are vague, this article just needs to pick one, lay out its reasoning, make explicit what's ruled in or out, and note that there are other common definitions. David.Throop 17:37, 5 January 2007 (UTC)[reply]

No it doesn't, that's precisely what should be avoided. The term is a vague one and there's not a lot any one person can do about that. If one narrow definition is used, it will bias the article. Showjumpersam 20:26, 14 June 2007 (UTC)[reply]

Lipids, fatty acids, and glycerides

For laymen, the beginning of the article does not explain the relationship between lipids, fatty acids, and glycerides. The reason for the second section would make more sense if it did. However, it does a good job of explaining the relationship between lipids and fats. Mdmcginn 19:48, 14 June 2007 (UTC)[reply]

unpolar

I have never seen this before - should be non-polar (or nonpolar)? --Anon

Thanks for catching that. --maveric149

Amphipathic? This makes no sense

You mean Amphiphilic right? I hope you dont mind if I make a few minor chances to make it more technically accurate. Jedi Dan

Amphipathic and amphiphilic are both correct and both mean that the molecule is part hydrophobic and part hydrophilic. GFP 06:15, 16 June 2006 (UTC)[reply]

Some people introduce a difference between amphipathic and amphiphilic :

amphipathic refers to molecule that are preferentially located at a polar-apolar interface. From this point of view, a phospholipid is amphipathic.
amphiphilic refers to compounds that can be solved in a polar or an apolar phase, but are not necessarely located at the interface.

-- hope it's help 136.159.234.84 20:42, 12 July 2006 (UTC)[reply]

Lipids are in the news this week,

and I thought this page should update to reflect... but don't have the time to do it now.

A quote

In the LIPID MAPS classification scheme, lipids are divided into eight primary categories: fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids, prenol lipids, saccharolipids, and polyketides. These categories are based on the functional backbone of the lipid molecule from a chemical standpoint. The categories are further subdivided into classes and subclasses to handle the existing and emerging arrays of lipid structures.

Source: [1]

I'll check back later, but perhaps someone with more biology than I can start to take a whack at that. JRice 21:28, 13 May 2005 (UTC)[reply]

Great idea. GFP 06:28, 16 June 2006 (UTC)[reply]

Question?

what is the primary physiological function of lipids: a. provide absorbtion of fat soluble vitamins b. conserve heat c. provide material for synthesis of hormones d. supply energy ???

How about e. all of the above? alteripse 03:37, 10 January 2006 (UTC)[reply]

Actually those are all quite minor (the absorbtion of fat soluble vitamines is almost irrelevant, the body doesn't need fat in it's intake to do this...). The major purpose is to build cellular membranes, followed closely by lipids as signalling molecules. Showjumpersam 20:30, 14 June 2007 (UTC)[reply]

Alpihatic, non-aromatic?

I am a chemistry novice and am a bit confused by this article. The intro says that "Lipids are one class of aliphatic hydrocarbon-containing organic compounds,"

and in the 'Structure' section we have:

"Some lipids are linear aliphatic molecules, while others have ring structures. Some are aromatic, while others are not."

Okay so far, perhaps, but in the 'Aliphatic compounds' article we have:

"In chemistry, aliphatic compounds are non-aromatic organic compounds"

There appears to be a contradiction here which somebody could maybe resolve.

Well, this all got quite mixed up. Aliphatic means not aromatic. Lipids are generally aliphatics, and the most popular (fatty acids, glycerides, etc.) are entirely aliphatic. But lipids can also have aromatic groups attached, for instance resorcilonic lipids, and they are then called alicyclic. Karol 12:46, 4 April 2006 (UTC)[reply]

Makes much more sense. Thanks for the edit, Karol. User:Kaplin 09:17, 5 April 2006 (UTC)[reply]

The thing that makes it hard to define a lipid is that it can have just about any structure, so long as it is a predominantly hydrophobic, hydrocarbon-based molecule. This should be clearer with the latest edits. GFP 06:25, 16 June 2006 (UTC)[reply]

Sorry, but aliphatic does not mean 'not aromatic'. Aliphatic refers to chains (which is usual for fatty acid residues) where aromatic refers to a particular type of delocalised pi system of electrons. There is such a thing as anti-aromatic. Colloquially, if a compound's primary functionality is aromatic, it will be referred to as such, but if it happens to contain a phenyl ring as a more minor piece of functionality it won't be referred to as aromatic as that would be misleading. I expect this is where the confusion originally came from and is quite understandable. Showjumpersam 20:36, 14 June 2007 (UTC)[reply]

Clean-up?

Does anyone know why the CleanUp tag is on this article? There's no discussion here on the Talk page as to why the tag is there, so it's hard to understand when it would be appropriate to remove it. If no one points out why the tag is there after a few days, and as long as nobody disagrees, I'm going to remove it. Cheerio! Mineralogy 08:24, 21 April 2006 (UTC)[reply]

Well, at the time I put the tag up, this page was more or less chaos. Now things are better, although still under my expectations. I myself haven't found the time to imprive this. I guess it would be Ok to take it down now. Karol 11:04, 22 April 2006 (UTC)[reply]

01:02, 9 May 2006 (UTC) I concur with "more or less chaos."

In the "Types of Fats" section, "eiconasoids" are listed next to unsaturated as though it is another name for unsaturated fatty acids. That's not even a little bit true. Could be a subheading under unsaturated, but even that is dubious.
This sentence is misleading:
"In nature, almost all double bonds in fatty acids are found in the cis configuration." You could say "the majority." Or you could explain that most fatty acids have at least one cis bond. However, trans bonds in fatty acids are quite common. Most linoleic acid is a hybrid of one cis, one trans bond.
Jedi Dan "fixed" amphipathic to say amphiphilic, but most biochemistry texts use amphipathic in that context; it should be changed back. It is linked; people can look it up if they are unclear.
There is a subheading "fatty acids" followed by "other", but "other" includes sentences which are explicity about fatty acids.
The section on Public Health is not very well written and is better covered and maintained elsewhere.
In general, the prose is uneven.

EEsterling

I just performed extensive cleanup and restructuring. I also corrected a lot of factual errors that had crept in since I last checked out this page and added some information. GFP 05:48, 16 June 2006 (UTC)[reply]

man that's a ghetto-looking picture compared to the other organic groups. ays 04:34, 27 September 2006 (UTC)[reply]

Reasons for GA Delisting

This article's GA status has been revoked because it fails criterion 2. b. of 'What is a Good Article?', which states;

(b) the citation of its sources using inline citations is required (this criterion is disputed by editors on Physics and Mathematics pages who have proposed a subject-specific guideline on citation, as well as some other editors — see talk page).

LuciferMorgan 01:04, 9 November 2006 (UTC)[reply]

i have no time to fix

OMG this article is crap unencyclopedic makes no sense —Preceding unsigned comment added by 203.27.153.35 (talk)

i agree. i rewrote the intro but the whole article needs organization and work. now that i'm on the topic, the phospholipid pages are also pretty abysmal. considering how fundamental these molecules are to life this should really be a priority. Roadnottaken 20:19, 6 July 2007 (UTC)[reply]

Lipid factor

Lipid factor is the percentage of vegoil in relation with the algae cells needed to get it. I.e., if the algae lipid factor is 40%, one need 2.5 kg of algae cells to get 1 kg of oil.

Is this useful? Tim Vickers (talk) 14:55, 11 July 2008 (UTC)[reply]

KDO structure is wrong

The KDO structure has 9-carbons. That is wrong it should have EIGHT since it is an octulosonic acid derived from a ketooctose. --kupirijo (talk) 00:48, 24 October 2008 (UTC)[reply]

So you're saying that in the upper rings shown in red at Image:Kdo2 lipidA.png the side chain should have 2 carbons, rather than three? Tim Vickers (talk) 15:23, 24 October 2008 (UTC)[reply]

Yes --kupirijo (talk) 01:29, 25 October 2008 (UTC)[reply]

Is Image:Kdo2-lipidA.png correct? Tim Vickers (talk) 15:30, 24 October 2008 (UTC)[reply]

With respect to #carbons it looks OK. It is an octulosonic acid as you know. 5 in the ring + 1 carboxyl + 2 in the side chain you corrected. Thanks. --kupirijo (talk) 01:29, 25 October 2008 (UTC)[reply]

Diet and Saturated fats

The last paragraph of this article when I accessed it was highly dubious and tendentious. It promotes an argument which proceeds to conclusions that are not widely held, and used highly selective citations to support this. I think to be fair, these should either be removed or balanced with other information.

The claim that, "High fat intake contributes to increased risk of obesity, diabetes and atherosclerosis" is not well supported in the literature. Perhaps the Nutrition Source from the Harvard School of Public Health is a better source as it includes data from several large trials (which are conspicuously not cited here). The claim that high fat intake leads to increased risk of diabetes is supported by only a single paper which primarily assessed survey data from patients who were already obese and diabetic. Hardly evidence that a high fat diet increases risk of diabetes.

I have removed this section as it is very poor information. The field of nutrition is highly contentious and Balkanized. The goal of wikipedia should be to present all sides of an issue. This paragraph does not achieve that, and in fact seems designed to promote one particular (and highly dubious) point of view, using unethical scholarship practices. Michaplot (talk) 23:05, 4 March 2009 (UTC)[reply]

I've reverted your removal - please achieve conensus on this talk page before removing large parts of an article, and also please use an edit summary - otherwise it can look like vandalism. Pedro : Chat 23:11, 4 March 2009 (UTC)[reply]

The section I removed was removed so as to give someone a chance to either improve it and reinsert or to put up a warning box. If I can figure out how to do that I will. The paragraph as written is bad, bad, bad.Michaplot (talk) 23:19, 4 March 2009 (UTC)[reply]

Evidence for impact of dietary fatty acids on cardiovascular health

This last paragraph of this page makes me ashamed to promote wikipedia. It is nearly all bad. For example, the assertion that, "A substantial amount of scientific evidence supports the impact of dietary fatty acids on cardiovascular health.[29]" is apparently based on a single only moderately applicable paper from nearly 20 years ago. To cite a 20 year old paper in a rapidly advancing field to support a contested notion is mischief. It is inaccurate--and shameful.

The Nutrion Source (www.hsph.harvard.edu/nutritionsource) says:

"Eat a low-fat, low-cholesterol diet" has been the mantra for healthful eating for decades. Touted as a way to lose weight and prevent or control heart disease and other chronic conditions, millions of people have followed (or, more likely, have tried to follow) this advice. Seeing a tremendous marketing opportunity, food companies re-engineered thousands of foods to be lower in fat or fat free. The low-fat approach to eating may have made a difference for the occasional individual, but as a nation it hasn't helped us control weight or become healthier. In the 1960s, fats and oils supplied Americans with about 45 percent of their calories; (1) about 13 percent of us were obese and under 1 percent had type 2 diabetes, a serious weight-related condition. Today, Americans take in less fat, getting about 33 percent of calories from fats and oils; (1) yet 34 percent of us are obese and 8 percent have diabetes, most with type 2 diabetes. (4, 5)
Why hasn't cutting fat from the diet paid off as expected? Detailed research—much of it done at Harvard—shows that the total amount of fat in the diet isn't really linked with weight or disease. [emphasis mine]

I tried to remove this section but was prevented by Pedro. I was told to provide reasons here (which I had done) and then to get consensus. I contend that the health information in this article needs some attention. Does anyone agree?Michaplot (talk) 23:53, 4 March 2009 (UTC)[reply]

Hi, Michaplot. I see your point regarding the paragraph in question, but deleting an entire large section is generally considered to be poor form unless it's completely unsalvageable (i.e., it is patent nonsense, or nearly so). A preferable approach would be for you to correct the shortcomings that you find. After all, if we simply deleted everything that was less than perfect here on Wikipedia, we wouldn't have much Wikipedia left! – Clockwork Soul 04:05, 5 March 2009 (UTC)[reply]

Thanks ClockworkSoul. I see your point and agree, it is not good to delete wholesale for the sin of less than perfection. In this case, however, I think that the section would be hard to salvage and should likely be rewritten. For example, the opening sentence "High fat intake contributes to increased risk of obesity" should be rewritten to say something like, "Dietary fat has not been shown to contribute to obesity, despite the widespread perception that it does". It seems to me that to go through the paragraph and change every sentence to something completely different would produce a less coherent and readable text than to simply rewrite it based on the current science.

By the way, I think, since this is such a controversial topic that the rewrite should mention both points of view e.g., "while some studies have indicated a relationship between high fat diets and obesity, recent large scale studies have failed to support this link." But either way, it seems to me to be pretty much a total rewrite and not a tweaking of existing text.207.233.7.249 Michaplot (talk) 03:06, 6 March 2009 (UTC)[reply]

Proposed Changes to Nutrition and Health Section

I propose to change the 4th paragraph of this section from:

"High fat intake contributes to increased risk of obesity,[44][45] diabetes[46][47] and atherosclerosis.[48]"

to:

The relationship between dietary fat intake and health is currently controversial. While a few studies indicate increased risk of obesity,[44][45] diabetes[46][47] and atherosclerosis[48], a number of very large studies, including the Women's Health Initiative Dietary Modification Trial, an eight year study of 49,000 women, the Nurses' Health Study and the Health Professionals Follow-up Study, reveal no such link. [refs below] None of these studies suggested any connection between percentage of calories from fat and risk of cancer, heart disease or weight gain. The Nutrion Source, a website maintained by the Department of Nutrition at tha Harvard School of Public Health, says, "Detailed research—much of it done at Harvard—shows that the total amount of fat in the diet isn't really linked with weight or disease."

Beresford SA, Johnson KC, Ritenbaugh C, et al. Low-fat dietary pattern and risk of colorectal cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006; 295:643-54.

Howard BV, Manson JE, Stefanick ML, et al. Low-fat dietary pattern and weight change over 7 years: the Women's Health Initiative Dietary Modification Trial. JAMA. 2006; 295:39-49.

Howard BV, Van Horn L, Hsia J, et al. Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA. 2006; 295:655-66.

Michaplot (talk) 05:07, 12 May 2009 (UTC)[reply]

Thanks much for your input, your suggested change sounds reasonable. I'll check out the refs and try to update that whole section to reflect current thinking, as suggested in the GA review. Sasata (talk) 06:45, 12 May 2009 (UTC)[reply]

This is still not fully right. The atherosclerosis paper discuses saturaed fats rather than total, and the Howard, von Horn, Hsia et al paper shows a minimal yet significant weight loss with reduced total fat intake, so there isn't much of a one side says this other side says that (though some people exaggerate the finding that low-fat diet makes you lose a kg while others don't). I'll just axe the section, because I think it would have to rewritten. Narayanese (talk) 08:36, 21 May 2009 (UTC)[reply]

I am not sure I follow what you are saying here. The atherosclerosis paper IS the Howard BV, Van Horn L, Hsia J, et al. paper, isn't it? It does not discuss weight loss. As far as I can see it does not focus only on saturated fats. The paper says, "The intervention was designed to promote dietary change with the goals of reducing intake of total fat to 20% of energy intake (in kilocalories) by increasing intake of vegetables and fruits to at least 5 servings daily and of grains to at least 6 servings daily."

Can you show me what in the paper makes you think the focus is on saturated fats?

It is the Howard BV, Manson JE, Stefanick ML, et al. that discusses weight loss, and yes it does show a modest weight loss from a low fat diet relative to a non-intervention (control) group. However, the reason for citing this paper is the review it presents of the literature. The paper notes that:

"Three recent studies reported that individuals assigned to a hypocaloric low-carbohydrate diet (with high protein and fat content) lost more weight during a 6-month period than did those assigned to reduced-fat (25%-33%) diets14-16; however, in the study that was extended to 1 year, no differences in weight loss were demonstrated between the low-carbohydrate and low-fat diet groups after 12 months.14 Furthermore, in the Women's Health Initiative (WHI) Feasibility Study, women in the low-fat intervention group after 6 months lost weight compared with the usual diet control group.17 A recent comparison of 4 low-fat and high-fat diets showed that weight changes did not differ at 1 year,7 but an 18-month comparison of a low-fat and Mediterranean-style diet showed poorer adherence to the low-fat diet.18"

This clearly suggests that high fat diets do not lead to weight gain. The study described in the paper shows weight loss from a low fat diet, but does not compare this to a high fat diet, low carb diet. High fat diets also lead to weight loss, and are work better because people have an easier time following them. The point is the study contains a good list of references. Perhaps it is not the best reference for this wikipedia article.

I agree the section should be rewritten, but I think the revision, while not perfect and perhaps in need of clearer references was correct: the amount of fat in one's diet does not seem to have much if any effect on health or weight. So, I do not agree with you axing the whole section, rather than improving it.Michaplot (talk) 09:09, 23 May 2009 (UTC)[reply]

Good to see you're looking after the page. I meant the Mustad et al ahterosclerosis paper, which compares three normal-level fat diets with differing fractions of saturated fat, so we would need another source to say that someone had found association between total fat intake and cardiovascular disease. I didn't realise you were using the intro rather than results section of the weigh-gain Women's health intiative study, so I wouldn't mind putting it back in. Narayanese (talk) 09:53, 23 May 2009 (UTC)[reply]

Thanks for you contributions, Narayanese. I have been suffering from the end of the semester crunch and have not had time to add anything to this. I think you are right, the references could be better. This is such a controversial issue in nutrition, which as Gary Taubes points out in his article in Science (The Soft Science of Dietary Fat--I can send yo a PDF if you don't have access) is a field (nutrition that is) that has become highly Balkanized. There are entrenched positions, and at least some data supporting nearly anything you want to claim. I do think it is important to represent all valid positions on this issue. Perhaps wikipedia needs a page on Dietary Fat, which could explain the various camps and their claims more fully. In the present article, I think that the "fat is bad" group should be mentioned, but my reading of the literature is that this position is not much supported. As the Nutrition Source strongly says, the largest and best studies have all indicated that quantity of fat is not (much) correlated with any health impact (fatty acid type is, of course). I suggest that this notion should be presented as the current state of the research. However, this goes against a large investment by some very powerful groups in the notion that dietary fat is bad, so it is bound to be controversial. It is a fine line between giving all sides equal time, and fairly representing the current state of research. I will hopefully have some more time for this when I finish with the semester.Michaplot (talk) 20:04, 3 June 2009 (UTC)[reply]

I have access to Science and read the article, shuddered at the polarised debate. As for giving sides equal time, I wouldn't do that - better evidence and worse evidence shouldn't be presented as if they were equal. Narayanese (talk) 19:50, 4 June 2009 (UTC)[reply]

flash point smoke point and melting point

please give answer —Preceding unsigned comment added by 86.41.158.30 (talk) 09:59, 25 May 2009 (UTC) can anyone tell me what is the functional group of lipids? —Preceding unsigned comment added by 62.215.144.95 (talk) 11:54, 11 July 2009 (UTC)[reply]

Image broken?

Having just came to this page, there is a rather strange sentence at the top of the page which suggests there should be an image, however it appears to have been broken? My total inexperience with Wiki's makes it impossible for me to check for the problem myself, or fix it should it even exist. —Preceding unsigned comment added by 62.31.182.37 (talk) 12:23, 2 November 2009 (UTC)[reply]

Fixed. Sasata (talk) 13:43, 2 November 2009 (UTC)[reply]