amylase: an enzyme produced in saliva and in the pancreas that breaks down starch in carbohydrates into glucose and energy. We all have different levels because of our genes.
antibiotics: chemicals originally produced by bacteria to defend themselves that have been manufactured for humans to use against bacteria. No new antibiotic drugs have been produced in thirty years and many bacteria have evolved resistance.
antioxidant: any beneficial substance that can mop up harmful products generated by cells like free radicals.
bacteria: simple but highly flexible tiny and ancient microbes that exist in every part of the world as well as in all the cavities of our bodies. Most are harmless, a few are disease-causing (pathogenic) and many are helpful.
Bacteroidetes: a common class (or phylum) of bacteria in our guts (Bacteroides are a sub-branch) that change with our environment and diet (e.g. meat eating).
bifidobacteria: subtypes of bacteria, commonly probiotics, that are contained in milk products and yoghurt as well as breast milk. Generally considered healthy in Western guts.
BMI (body mass index): a formula that estimates your amount of body fat by dividing your weight in kilograms by your height in metres squared. E.g. a 70 kg male 1.80 metres tall has a BMI of 70/3.24 (1.80 × 1.80) = 21.6. Above BMI 25 is overweight, and over 30 is classified as obese. BMI is not very accurate in distinguishing muscle from fat.
butyrate: a healthy short-chain fatty acid (SCFA) produced by bacteria when they digest food in the colon containing fibre and carbs, especially polyphenols. It has antioxidant and anti-inflammatory properties and signals the immune system to act.
carnitine: made inside the body from amino acids, and important in helping to fuel the body. When digested it can raise levels of TMAO and increase the risk of heart disease. Used as a supplement by bodybuilders to burn fat and increase muscle, and is found in large amounts in meat.
cholesterol: a class of essential lipid that the body synthesises itself to keep our cells intact. It is transported around the body by lipoproteins. High blood levels of cholesterol roughly correlate with heart disease, but its risk has been exaggerated. Found in many foods, including fish and nuts. Healthy levels are regarded as below 5mmol/l but the average in the UK are around 6mmol/l.
Christensenella: an ancient bacteria that many people have in their guts that has been found to protect against obesity. Related to methane-producing bacteria.
Clostridium difficile (C. diff): a pathogenic bacteria that lives happily in the guts of 3 per cent of people until overdoses of antibiotics wipe out its competitors, at which point it grows rapidly and takes over in massive numbers. It can produce nasty toxins causing major gut damage (colitis). Often resistant to antibiotics, which just make it stronger. Often the only cure is a faecal microbial transplant (FMT).
colitis: inflammation of the colon caused by infections or auto-immune disease.
colon: the lower part of the intestines, where most of our bacteria and microbes live and digest the fibre-rich food that hasn’t been absorbed higher up in the small intestine.
diabetes: two diseases resulting from too much sugar (glucose) in the blood. The commonest is Type 2, which is related to obesity and to our genes and makes insulin ineffective, causing blood glucose to rise and excessive insulin to be produced in compensation.
DNA: Deoxyribonucleic acid is the building block of our genetic material; it is arranged as a double helix in 23 chromosomes and contains the roughly 20,000 genes in each cell of our bodies.
E. coli: a common bacteria that lives in our colons and can occasionally become pathogenic after infections or antibiotics.
endocrine: a term for anything producing hormones (e.g. thyroid or pancreas).
endocrine disruptors: chemicals that act epigenetically to alter hormones, e.g. the bisphenol (BPA) in plastic bottles.
epidemiology: the study of large groups or populations in order to discover the causes of disease.
epigenetic: describes mechanisms by which chemical signals can switch genes on and off without altering the DNA structure. A normal process in babies and growth, which can be altered by diet and chemicals for up to several generations.
fat: a term with many different meanings. Scientifically synonymous with lipids.
fibre: a term for the hard-to-digest parts of carbohydrates that reach the colon for our microbes to feed off. High levels are found in fruit, legumes, other vegetables, whole grains and nuts. Artificial fibre is also available as additives.
Firmicutes: a major group (phylum) of our gut microbes that contains many of the species related to health and disease and is partly influenced by our genes.
FMT: a polite term for faecal microbial transplant, whereby a healthy donor’s stool is placed via tubes or tablets into the colon of the recipient.
free radicals: small chemicals released from cells as part of their normal function. If they accumulate they can be harmful to the body. Mopped up by antioxidants.
fructose: a carbohydrate sugar that makes up 50 per cent of table sugar and is much sweeter. Contained in most fruits and can be produced artificially from corn syrup and used in soft drinks.
fungi: a large group (kingdom) of ancient organisms that include yeast, mould and mushrooms.
gene: a small group of chemicals on our DNA that tell the body to make a particular protein. We have about 20,000 in each of our cells. Estimates vary as our precise definition of genes changes.
glycaemic index (GI): a measure of the speed at which different foods produce an increase in glucose and then insulin in the blood. Low GI foods are the basis of many diets. High-GI foods enable sugars to be released rapidly and cause rapid peaks in blood glucose and insulin (e.g. mashed potatoes) as opposed to low-GI high-fibre foods like celery. It is still unclear how important this mechanism is for obesity.
HDL (high-density lipoprotein): a combination of a lipid and a protein that safely transports fats around the body. Measured in the blood to compare in a ratio with the unhealthy form, low-density lipoproteins (LDL).
heritability: the proportion of the variation in a trait due to genetic effects or, more precisely, the differences between people in a trait or disease that can be explained by genetic factors. Ranges from 0 to 100 per cent.
hypothalamus: an area at the base of the brain controlling the release of many hormones including those relating to emotion, stress and appetite.
IBS (irritable bowel syndrome): a common complaint with no commonly agreed cause. It produces altered bowel frequency, cramps and wind. Associated with abnormal gut microbes.
IGF-1: insulin growth factor 1 is a hormone implicated in many body functions, including the speed of ageing and repair. Has good evidence of increasing longevity in animals but not yet in humans.
inflammation: results from the way the body reacts to injury, infection or stress and is a normal response involving many different processes (e.g. after a bee sting). It usually causes leakiness of cell walls and the triggering of repair and defence cells, resulting in swelling, redness, pain, heat and loss of function.
insulin: the hormone which, in response to blood glucose, controls how much sugar to store as glycogen in the liver and fat in fat cells.
insulin resistance: results when insulin doesn’t rise as much after ingesting glucose, forcing the pancreas to produce more insulin so as to control glucose levels; leads to diabetes.
inulin: a chemical that acts as a strong prebiotic helping bacteria to multiply. Found in high concentration in artichokes, chicory, garlic, onions, and in small amounts in bread.
ketogenic diet: a diet that makes the body change from burning glucose as energy to burning ketones, which derive from protein and fat. Examples include high-protein/low-carb diets and fasting.
lactobacillus: a bacteria which breaks down lactose in milk and in other sugars into lactic acid. A key component in many foods, e.g. cheese, yoghurt and pickles.
leptin: a hormone released by the brain and closely related to body fat levels.
lipids: the scientific word for fats, but include many other molecules, e.g. fatty acids. When combined with proteins lipids are called lipoproteins, which travel around the body and can be of different shapes and sizes.
low-density lipoproteins (LDL): the less healthy form in which lipids are transported. They can get absorbed into blood vessels and lead to clogging of the arteries (atherosclerosis).
medium-chain triglycerides: contain medium-chain fatty acids that are different from human or cow’s milk. Are more ketogenic than other fats. Despite lack of evidence, believed by some to have health properties. Contained in palm and coconut oil.
meta-analysis: a technique for combining the results of different studies or trials to produce a single summary result. Provides better evidence than any single study, but can still be misleading if all the studies are biased.
metabolic rate: a measure of how rapid or slow energy input and output processes occur.
metabolism: the way the body and all cells both use and expend energy. Can be modified by many factors, e.g. heat, exercise, illness.
metabolomics: the study of the body’s metabolites, which are the chemical signatures of the cell. Believed to number around 3,000 in human blood.
microbe: an organism that can be seen only with the aid of a microscope; includes bacteria, viruses, yeast and some larvae and worms.
microbiome: the whole community of microbes that may be in our guts or mouths or in the soil.
neurotransmitters: chemicals in the brain that allow nerve cells (neurons) to communicate and control mood (e.g. serotonin, dopamine).
observational study: a type of epidemiological research that makes inferences by comparing risk factors (e.g. food) with outcomes like disease. Evidence is weak when cross-sectional but better when people are followed over long periods (prospective observational study, or cohort study). All observational studies can be biased.
oil: a type of lipid (fat) that is liquid at room temperature.
oleic acid: a fatty acid (mono-unsaturated) that is one of the major components of olive oil.
omega 3 fatty acid: also called ω-3, this is a polyunsaturated fatty acid with a double bond at the 3rd carbon. Contained in many oily fish and often used as a (much hyped) health supplement for the heart and brain. It is an essential fatty acid that we can’t make ourselves.
omega 6 fatty acid: also called ω-6, this is a polyunsaturated fatty acid with a double bond at the 6th carbon. Contained in many foods e.g. soybean, palm oil, chicken, nuts and seeds, and is an essential fatty acid. Has a bad (unfounded) reputation.
polyphenols: a group of many chemicals released from food after digestion by microbes, many of which are useful and healthy. Polyphenols include flavonoids and resveratrol, which have antioxidant properties. Contained in vegetables, fruits, nuts, tea, coffee, beer and wine.
polyunsaturated fatty acids (PUFA): a type of lipid that consists of long-chain fatty acids with double bonds, and that are part of many foods generally regarded as healthy.
prebiotic: any food component that encourages healthy bacteria to flourish like a fertiliser. Bacteria often feed off prebiotics. Often contains inulin, which is found in high levels in Jerusalem and globe artichokes, celery, garlic, onions and chicory root.
PREDIMED study: a Spanish clinical study which randomly allocated over 4,000 patients to a low fat diet or a classical Mediterranean diet and followed them for four years. They found the Mediterranean diet was superior in reducing heart disease, diabetes and weight gain.
Prevotella: a group of bacteria that flourishes in vegetarians and is rare in meat eaters. Generally regarded as a marker of a healthy diet.
probiotic: a group of bacteria added as a food supplement. Believed to provide health benefits.
PROP (6-N-Propylthiouracil): a chemical tasting either very bitter or tasteless, depending on your genetic make-up. Used to test taste in experiments.
randomised controlled trial: an RCT is the gold standard for evidence in epidemiology. Subjects are randomly allocated to the test treatment or diet and compared to another standard treatment or a placebo, then followed for months or years (cf. PREDIMED study).
resveratrol: a type of polyphenol naturally found in food and wine that in animals has healthy anti-ageing properties. Large amounts need to be ingested to be beneficial; side effects from overdose have been reported.
saturated fat: a type of lipid that lacks hydrogen bonds and is contained in large amounts in oils like coconut and palm oil, dairy and meats. Previously thought to be harmful.
sequencing: a term for identifying all the key parts of DNA and genes in an organism. Usually the DNA is broken into millions of small pieces and reassembled (often referred to as ‘shotgun’). Used to identify microbe species and disease genes in humans in great detail.
sugar: another common word for soluble carbohydrates; or refers to the white powder we eat called sucrose, which is a mix of glucose and fructose. The suffix -ose means that the chemical is a sugar (e.g. lactose).
TASR1 and TASR2: the major taste-receptor genes that are expressed by taste receptors found all over the oral cavity and that influence how we perceive sweet and bitter tastes.
TMA and TMAO: trimethylamine is a chemical in meat and large fish that is converted in the gut by microbes into the oxidised form, TMAO, which accelerates atherosclerosis and heart disease.
trans fats: also called hydrogenated fats, these are chemically transformed unsaturated fats that are easy to cook with but hard to break down in the body. Common as dairy substitutes and in junk foods. Major cause of heart disease and cancer. Banned in some countries and slowly being phased out in others.
Treg cell: an important type of immune cell (T-suppressor regulatory cell) that keeps the immune response in check and has two-way communication with gut microbes.
umami: the fifth (savoury) taste sense that mimics meat and comes from glutamate and is found in mushrooms. There is now a possible sixth sense called ‘kokumi’, meaning ‘heartiness’.
viruses: tiny microbes that outnumber bacteria 5 to 1, and many feed off them (these devourers are called ‘phages’) to control their numbers. Most are harmless to us and live in our bodies and may have a health role.
visceral fat: the internal fat that accumulates around your intestines and liver. Excess fat is associated with heart disease and diabetes. More harmful than fat on the exterior of the body.
vitamins: molecules that are essential for the body’s chemical reactions to work. We get most from food, sunlight (vitamin D) and our gut microbes.
yeast: a member of the fungi kingdom that converts sugar into alcohol and carbon dioxide. Used in making bread and alcohol. May promote healthy gut microbes. Can happily live in our guts and is only rarely pathogenic, e.g. candida infections.