Alpha-linolenic acid: An omega-3 fatty acid found in some plants and seed oils, such as flaxseed, canola, and soybean oils. It is also present in English walnuts. Alpha-linolenic acid is considered essential because we humans need it (or its long-chain derivatives) and cannot make it on our own. It has 18 carbons and 3 double bonds. Alpha-linolenic acid can be converted to EPA and to a lesser extent, DHA in humans, but the conversion is very inefficient. Most alpha-linolenic acid is oxidized or “burned” for energy.
Amyloid plaque: Deposits of beta-amyloid protein that accumulate outside the neurons of the brain under abnormal conditions, such as Alzheimer’s disease.
Arachidonic acid: An omega-6 fatty acid derived from the conversion of linoleic acid. It has 20 carbons and 4 double bonds. Arachidonic acid is metabolized to eicosanoids, a family of substances highly active in immune and inflammatory responses. Arachidonic acid also stimulates blood clotting and is an essential component of brain cells.
Cell signaling: The transfer of information from one cell to another. Cells have various ways of communicating with each other, including direct cell contact and chemical signals carried by transmitter substances. These include such things as hormones, small molecules like cyclic AMP and acetylcholine, and enzymes such as protein kinases and phosphatases.
Cytokines: Chemical messenger molecules used by immune and nerve cells to communicate with one another and other cells.
DHA (Docosahexaenoic acid): A long-chain omega-3 fatty acid found primarily in fish and shellfish (shown left). A small amount can be made from the conversion of EPA, but humans cannot make DHA from scratch. DHA has 22 carbons and 6 double bonds. It is essential for brain growth and function. It is also the precursor for various substances that protect brain cells (neuroprotectins) and control immune responses (resolvins).
Double bond: The point in a fatty acid carbon chain where two hydrogen atoms have been lost. The location of the first double bond in a fatty acid with more than one double bond is determined by counting the number of carbons from the non-acidic end of the fatty acid. For example, omega-3 fatty acids have their first double bond three carbons from the “omega” end of the fatty acid.
Eicosanoids: A family of highly active substances derived from arachidonic acid or EPA and DHA that affect immune and inflammatory responses. They include prostaglandins, thromboxanes, and leukotrienes. Those made from arachidonic are generally pro-inflammatory, whereas those from EPA are anti-inflammatory.
EPA (Eicosapentaenoic acid): A long-chain omega-3 fatty acid found primarily in fish and shellfish. A small amount can be made from the conversion of alpha-linolenic acid to EPA. EPA has 20 carbons and 5 double bonds. Humans cannot make EPA from scratch.
Essential fatty acids: These are polyunsaturated fatty acids the human body needs and cannot make for itself or derive from other fatty acids. Linoleic acid (omega-6) and alpha-linolenic acid (omega-3) are usually considered essential because they cannot be made in the body, but can be converted to long-chain forms, which are usually the most critical to the body’s needs.
Fat: The common name for triglyceride. It is the storage form of fatty acids and is the main substance in food fats and oils and in the body’s fat tissue.
Fatty acid: A chain of carbon atoms with hydrogen atoms attached to them. Each fatty acid has an acidic or carboxyl end and an omega end containing only hydrogens. Three fatty acids attached to glycerol make a triglyceride or fat.
HDL: High-density lipoprotein or “good” cholesterol. It is about half triglyceride and cholesterol with the rest being protein. It is believed to transport cholesterol away from tissues to the liver for disposal. High levels – above 60 mg/dl – are considered protective against heart disease.
LDL: Low-density lipoprotein or “bad” cholesterol. This is a lipoprotein with more cholesterol than protein, which carries cholesterol from the liver to the rest of the body. Because it deposits cholesterol on the walls of arteries, it is considered bad. High levels of LDL increase the risk of heart disease. Levels below 100 mg/dl are optimal and above 130 mg/dl borderline high.
Linoleic acid: A polyunsaturated fatty acid of the omega-6 family, essential for human growth and development. Linoleic acid has 18 carbons and 2 double bonds (shown left). It is the main polyunsaturate fat in the western diet. It can be converted to long-chain fatty acids, principally arachidonic acid.
Lipids: A general term for substances that usually dissolve in organic solvents, but generally not in water. Lipids include fats, fatty acids, sterols, phospholipids, glycolipids, waxes, and others. They are essential components of every cell membrane.
Lipoprotein: A combination of fat and protein that transports lipids (fats, cholesterol) in the blood.
Long-chain: Refers to fatty acids having 20 or more carbon atoms.
Marine omega-3s: Refers mainly to EPA and DHA, long-chain omega-3s found almost exclusively in fish and shellfish and some eggs.
Monounsaturated: A fatty acid missing one pair of hydrogens so that it has one double bond. A common example is oleic acid.
Neuron: Also called nerve cells, neurons process and transmit information by generating and propagating electrical signals.
Neuroprotectin D1: A derivative of DHA produced by neurons and retinal pigment epithelial cells. Neuroprotectin D1 has potent anti-inflammatory properties, prolongs neuronal cell survival, and protects neurons against toxicity from other substances such as the amyloid protein of Alzheimer’s disease.
Neurotransmitters: Chemicals that relay, amplify and modulate electrical signals between a neuron and another cell. These include substances such as amino acids (e.g., glutamic acid, glycine), peptides (e.g., vasopressin, neurotensin), monoamines (e.g., norepinephrine, dopamine, serotonin) and acetylcholine. Polyunsaturated fatty acids also participate in neurotransmission.
Omega-3: A fatty acid in which the first double bond or pair of missing hydrogens occurs 3 carbons away from the omega or non-acidic end of the fatty acid. Marine omega-3s refers mainly to EPA and DHA, also called long-chain omega-3 fatty acids because they have 20 or more carbons in their chain.
Omega-6: A fatty acid in which the first double bond or pair of missing hydrogens occurs 6 carbons away from the omega or non-acidic end of the fatty acid. The most common omega-6 fatty acid in food is linoleic acid; in cell membranes, it is arachidonic acid.
Photoreceptor: A specialized neuron that absorbs light and converts that energy into a signal that alters the membrane potential of the cell, thereby initiating the transmission of a nerve signal.
Plaque: A common name for the build-up of fatty deposits in the walls of arteries, particularly of the heart and carotid artery to the brain. These are also called atheroma. Plaque consists of cholesterol, triglycerides, phospholipids, macrophages, a type of immune cell, fibrous tissue, protein, calcium, muscle tissue, and other components. For information on the plaque that accumulates in Alzheimer’s disease, see “amyloid plaque.”
Polyunsaturated: A fatty acid with two or more double bonds. Common polyunsaturated fatty acids are linoleic, alpha-linolenic, arachidonic, eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids.
Prostaglandins: Substances made from arachidonic acid and EPA that have strong physiological effects, such as the constriction or relaxation of vascular smooth muscle, aggregation of platelets, and pain in spinal neurons.
Trans fatty acid: An unsaturated fatty acid with a slightly different shape (configuration) from the usual unsaturated fatty acid. Trans fatty acids are straighter than their “cis” counterparts, so they behave more like saturated fatty acids.
Triglyceride: A molecule consisting of 3 carbon atoms (glycerol) each with a fatty acid attached to them. They are the storage form of fat.
Unsaturated: A term applied to fatty acid to denote the presence of one or more double bonds – the loss of two hydrogens from the fatty acid chain. The more double bonds, the more unsaturated the fatty acid. Two or more double bonds define a fatty acid as polyunsaturated.