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Category: Metabolims

Fat Soluble Vitamins

April 26, 2020 10:20 am

Written By: Maria Vardapetyan, Eric Baghdasaryan, Osheen Abnous

Vitamins are chemicals that facilitate many processes in the human body such as blood clot formation, good vision, fight infections etc. There are two classes of vitamins. Water soluble vitamins and fat soluble vitamins. Water soluble vitamins dissolve in water. This makes it possible for them to be absorbed through all mucous membranes. Fat soluble vitamins on the other hand do not dissolve or pass through mucous membranes. Fat-soluble vitamins are absorbed in the intestine along with fats in the diet. These vitamins have the ability to be stored in the fat tissues of the human body. Water-soluble vitamins are not stored in the body and have to be taken in daily with the food and dietary supplements. Solubility of a vitamin is not a function of its physical state. There are fat soluble vitamins that have a liquid form and almost all of the water soluble vitamins come in form of pills or powders.

In this article, we are going to focus on fat soluble vitamins. They are all complex molecules made of carbon, hydrogen, and oxygen in different arrangements (see figures 1, 2, 3 and 4). These fat soluble vitamins are vitamin A, D, E and K.

Vitamin A

Vitamin A has a major role in vision, immune function, cell growth, and maintenance of organs such as heart, kidneys, lungs, etc. It plays a pivotal role in the health of our eyes, specifically the retina1. Rhodopsin protein, a major protein that has the leading role in the process of vision, is found in the retina where it allows us to perceive light. This protein requires vitamin A to function properly. Without vitamin A, rhodopsin cannot sense light and thus cannot initiate the process by which vision occurs.

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Figure 1: Chemical structure of Vitamin A molecule

 

Vitamin D

Vitamin D regulates different chemical reactions that are associated with bones, muscles, and the immune system. The simplified way it does this regulation is it helps absorb calcium from dietary nutrients which in turn strengthens the bones, helps neurons exchange signals to move muscles and helps the immune system to fight against viruses and bacteria2. 

pastedGraphic_1.pngFigure 2: Chemical structure of Vitamin D molecule

Vitamin E

Vitamin E acts as an antioxidant. Antioxidants are naturally occurring chemicals that neutralize toxic byproducts of many chemical reactions in the human body. When food is consumed and digested, the human body converts it into energy. As a result of metabolism free radicals (toxic byproducts) are formed and are neutralized with the help of vitamin E. In addition, free radicals are also in the environment. Furthermore, vitamin E stimulates the immune system to fight against bacteria and viruses3.

pastedGraphic_2.pngFigure 3: Chemical structure of Vitamin E molecule

Vitamin K

Vitamin K can be obtained from food and dietary supplements. There are two forms of vitamin K: phylloquinone (Vitamin K1), which is found in spinach, kale and other greens and menaquinone-4 (Vitamin K2), which is found in animal products. Vitamin K1 is involved in blood clotting, and Vitamin K2 is involved in bone tissue building. Vitamin K1 is the main Vitamin K in human diet (75-90% of all vitamin K consumed), however, it is poorly absorbed in the body4,5. 

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Figure 4: Chemical structures of Vitamin K1 and K2 molecules

Absorption of fat soluble vitamins

Polarity describes the inherent charge(positive or negative) or lack of charge for any given substance or molecule.  Molecules that are charged are referred to as “polar”, while those that lack charge are “nonpolar”. When discussing solubility, it is important to remember the phrase “like dissolves like”. That means polar (charged) substances like to interact with a polar environment like water, since water contains a slight negative charge. Hence, charged substances are water-soluble. Nonpolar substances on the other hand readily interact with nonpolar environments such as fat, which contains no charge. Therefore, molecules that lack a charge such as vitamins A, D, E, and K are referred to as fat soluble. 

 

Due to their water fearing nature, these fat soluble vitamins cannot simply be absorbed directly into the bloodstream (which is mostly water) like the sugars and amino acids in our diet. As their name suggests, these fat soluble vitamins like to be embedded in fatty droplets, which facilitate their absorption in the following way. Fat soluble vitamins group together with other fat molecules to form fatty droplets, effectively reducing the amount of interaction with the watery environment of the intestines. Therefore, without an adequate amount of fat in your diet, your body is unable to effectively absorb these fat-soluble vitamins. This may be true in an intact anatomy, however, post weight loss surgical patients can not increase their fat soluble vitamin levels by increasing their fat intake. This is due to the fact that a high fat diet causes excessive bowel movement which in turn washes away any vitamins taken by mouth. DS limits fat absorption (thus the great weight loss) which can cause vitamin A and D deficiency that can not be easily corrected with oral supplementation.

As mentioned before, fat soluble vitamins are hydrophobic and nonpolar, which means they are also fat loving or lipophilic. Excess fat soluble vitamins can be stored in the liver and fat tissue. Therefore, these vitamins do not need to be eaten every single day since stores of these vitamins can sustain a person for some time. It may take several weeks or months for our body to deplete these stores of fat soluble vitamins which is why it generally takes a longer amount of time for fat soluble vitamin deficiencies to manifest themselves. The ability to store these fat soluble vitamins in tissues can also lead to vitamin toxicity – marked by an excess of vitamin stores in our body. 

Clinical manifestations of A, D, E, K deficiency

Vitamin Clinical Deficiency manifestations
Vitamin A Vision Problems

Night blindness 

Dryness of the eye

Vitamin D Softening and weakening of the bones

Decreased bone formation 

Bone shape distortion

Bowed legs (generally in children)

Hypocalcemia 

Vitamin E Damage to red blood cells 

Tissue/organ damage due to inability to supply enough blood

Vision problems

Nervous tissue malfunction

Vitamin K1  Excessive bruising

Increased bleeding time

Small blood clots under nails

Increased bleeding in mucous membrane

Vitamin K2  Weak bones

Increased plaque deposits along gumline

Arterial calcification

 

 

References

  1. Office of Dietary Supplements – Vitamin A. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/#. Accessed April 26, 2020.
  1. Office of Dietary Supplements – Vitamin D. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminD-Consumer/. Accessed April 26, 2020.
  1. Office of Dietary Supplements – Vitamin E. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminE-Consumer/. Accessed April 26, 2020.
  1. Vitamin K. The Nutrition Source. https://www.hsph.harvard.edu/nutritionsource/vitamin-k/. Published July 2, 2019. Accessed April 26, 2020.
  1. Beulens JWJ, Booth SL, van den Heuvel EGHM, Stoecklin E, Baka A, Vermeer C. The role of menaquinones (vitamin K₂) in human health. The British journal of nutrition. https://www.ncbi.nlm.nih.gov/pubmed/23590754. Published October 2013. Accessed April 26, 2020.

100% Fruit Juices and Risk of Cancer

April 16, 2020 8:54 pm

We have talked about the excess free calorie that is present with fruit juices. Now there is proven research article demonstrating the connection between surgary drinks and the increased risk of cancer. This study

This study is significant for a number of reasons: It is a very large study with over a 100,000 subjects studied. Furthermore, it was specifically looking for association between nutrition and health.

The conclusion of this research article is self explanatory. Eliminating or cutting down high sugary drinks is an easy way of reducing cancer risk factors. The study also states that there were no identifiable association between the artificial sweeteners and cancer risks. However, this conclusion was not statistically significant. The relationship between sweeteners and cancer have been studied extensively in the past and we’ve shared several of them.

Protein Sources

May 16, 2019 10:26 am

Not all proteins are created equally. The protein that we digest serves as the source of the essential amino acids, (the building blocks which make up a protein). The essential amino acids can not be made in out body. Protein sources can be animal or plant based.  We’ve written a in-depth explanation of protein sources in this previous blog: Protein Optimization

The proteins can also be decided into two categories:

1-High quality  or Complete proteins

Complete proteins contain all the indispensable amino acids that we need. Animal based proteins for the most part are complete proteins. These include cheese, mean, fish, mild, yogurt, egg and poetry.

 

2-Low quality or Incomplete proteins

Incomplete protein are mostly plant based proteins. In most cases, the incomplete proteins either lack or have insufficient about of the one or a number of amino acids to be able to satisfy our nutritional requirements.

This is why we general recommend animal based proteins.

Following weight loss surgery there are some guidelines that can be helpful in our previous blog: Importance of Protein.

There is also much discussion on whey protein. There is a brief and good explanation on this subject here.

Recipes for protein shakes.

 

 

Absorption of Minerals and Metals

January 12, 2009 6:42 am

The vast bulk of mineral absorption occurs in the small intestine. The best-studied mechanisms of absorption are clearly for calcium and iron, deficiencies of which are significant health problems throughout the world.

Minerals are clearly required for health, but most also are quite toxic when present at higher than normal concentrations. Thus, there is a physiologic challenge of supporting efficient but limited absorption. In many cases intestinal absorption is a key regulatory step in mineral homeostasis.

Calcium

The quantity of calcium absorbed in the intestine is controlled by how much calcium has been in the diet during recent periods of time. Calcium is absorbed by two distinct mechanism, and their relative magnitude of importance is set by dietary calcium “history”:.

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Cellular Iron Absorption
  1. Active, transcellular absorption occurs only in the duodenum when calcium intake has been low. This process involves import of calcium into the enterocyte, transport across the cell, and export into extracellular fluid and blood. Calcium enters the intestinal epithelial cells through voltage insensitive channels and is pumped out of the cell via a calcium- ATPase.The rate limiting step in transcellular calcium absorption is transport across the epithelial cell, which is greatly enhanced by the carrier protein calbindin, the synthesis of which is totally dependent on vitamin D.
  2. Passive, paracellular absorption occurs in the jejunum and ileum, and, to a much lesser extent, in the colon when dietary calcium levels have been moderate or high. In this case, ionized calcium diffuses through tight junctions into the basolateral spaces around enterocytes, and hence into blood. Such transport depends on having higher concentrations of free calcium in the intestinal lumen than in blood. Additional Calcium information here.

Phosphorus

Phosphorus is predominantly absorbed as inorganic phosphate in the upper small intestine. Phosphate is transported into the epithelial cells by contransport with sodium, and expression of this (or these) transporters is enhanced by vitamin D.

Iron

Iron homeostasis is regulated at the level of intestinal absorption, and it is important that adequate but not excessive quantities of iron be absorbed from the diet. Inadequate absorption can lead to iron-deficiency disorders such as anemia. On the other hand, excessive iron is toxic because mammals do not have a physiologic pathway for its elimination. Iron is absorbed by villus enterocytes in the proximal duodenum. Efficient absorption requires an acidic environment, and antacids or other conditions that interfere with gastric acid secretion can interfere with iron absorption.

Ferric iron (Fe+++) in the duodenal lumen is reduced to its ferrous form through the action of a brush border ferrireductase. Iron is the co-transported with a proton into the enterocyte via the divalent metal transporter DMT-1. This transporter is not specific for iron, and also transports many divalent metal ions.

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Once inside the enterocyte, iron follows one of two major pathways. Which path is taken depends on a complex programming of the cell based on both dietary and systemic iron loads:

  1. Iron abundance states: iron within the enterocyte is trapped by incorporation into ferritin and hence, not transported into blood. When the enterocyte dies and is shed, this iron is lost.
  2. Iron limiting states: iron is exported out of the enterocyte via a transporter (ferroportin) located in the basolateral membrane. It then binds to the iron-carrier transferrin for transport throughout the body.

Iron in the form of heme, from ingestion of hemoglobin or myoglobin, is also readily absorbed. In this case, it appears that intact heme is take up by the small intestinal enterocyte by endocytosis. Once inside the enterocyte, iron is liberated and essentially follows the same pathway for export as absorbed inorganic iron. Some heme may be transported intact into the circulation. Additional Iron information here.

Copper

There appear to be two processes responsible for copper absorption – a rapid, low capacity system and a slower, high capacity system, which may be similar to the two processes seen with calcium absorption. Many of the molecular details of copper absorption remain to be elucidated. Inactivating mutations in the gene encoding an intracellular copper ATPase have been shown responsible for the failure of intestinal copper absorption in Menkes disease. A number of dietary factors have been shown to influence copper absorption. For example, excessive dietary intake of either zinc or olybdenum can induce secondary copper deficiency states. Additional Copper information here.

Zinc

Zinc homeostasis is largely regulated by its uptake and loss through the small intestine. Although a number of zinc transporters and binding proteins have been identified in villus epithelial cells, a detailed picture of the molecules involved in zinc absorption is not yet in hand. Intestinal excretion of zinc occurs via shedding of epithelial cells and in pancreatic and biliary secretions. A number of nutritional factors have been identified that modulate zinc absorption. Certain animal proteins in the diet enhance zinc absorption. Phytates from dietary plant material (including cereal grains, corn, rice) chelate zinc and inhibit its absorption. Subsistence on phytate-rich diets is thought responsible for a considerable fraction of human zinc deficiencies. Additional Zinc Information here