Celebrities of nutrition evoke feelings of awe, envy and adulation in many of us. While the Gwyneth Paltrows of the group first achieve celebrity status in other fields, others first make a name for themselves in food and nutrition, despite not having formal nutrition qualifications. Think Pete Evans, Sarah Wilson and Belle Gibson, whose nutrition empire has crumbled over the past week.

Nutrition celebrities often promote “fad diets”, which are strict diets that often eliminate entire food groups and don’t have a solid scientific basis. In fact, they often demonstrate a misunderstanding of biochemistry and other basic nutrition science.

The Paleo Way by Pete Evans forbids grains, legumes, dairy and coffee, among other things. Evans’ website claims “Paleo is all about balance”, but in reality, is anything but balanced.

Before Belle Gibson’s cancer diagnosis was questioned, she touted “clean eating”, discouraging the consumption of gluten, dairy and genetically modified foods, among other things. She promoted “detoxing”, which involved “alkalising your system” by drinking lemon water, and recalibrating “your digestive and immune system” by cutting out fruits such as bananas and apples.

Sarah Wilson “quit sugar” and recommends cutting out fruit for the first few weeks of her eight-week I Quit Sugar program because it “allows you to break your sugar addiction and for your body to recalibrate”.

It’s no surprise that the British Dietetic Association listed the paleo diet and the sugar-free diet as two of their top five worst celebrity diets.

When it comes to healthy eating, we know what works. The Australian Dietary Guidelines may not sound as sexy as these fad diets, but they’re the result of painstaking work to summarise the best scientific evidence on what constitutes a healthy diet and how diet can promote health.

So why do nutrition celebrities have so much pull? And what impact might it have?

The good

Nutrition celebrities have done some good in the world. They have undoubtedly changed the nutrition habits of some of their followers for the better. This might include increasing their intake of fruits and vegetables, abandoning added sugar- and salt-laden foods such as some breakfast cereals, and helping followers who are overweight or obese to lose weight.

These changes are of particular importance when you consider the high rate of excess weight and obesity and the low intake of good foods like vegetables in the Australian population.

The bad

The negative effects of celebrity nutrition range from public confusion about what is good to eat and drink, to death.

A trusting, vulnerable and adoring member of the public might just decide that Belle Gibson is right – who needs modern medicine for cancer? Gibson claimed she cured her multiple cancers through alternative means. Jessica Ainscough, founder of the Wellness Warrior, died prematurely last month after choosing alternative cancer therapy that included endless juices and coffee enemas.

Belle Gibson’s book, The Whole Pantry, has been pulled from circulation in Australia and the US launch of the book next month has been cancelled. Her “health, wellness and lifestyle” app has also been pulled from Australian and US app stores.

Also this week, Pete Evans’ Bubba Yum Yum DIY baby milk, which is composed of blended liver and bone, has attracted criticism that it could risk the health of babies. This broth provides toxic levels of micronutrients such as vitamin A. This can cause permanent damage and even death.

While Evans’ publisher Pan McMillan has announced it will not be releasing the book, Evans plans to release it as an e-book.

Followers of celebrity nutrition advice may become unnecessarily strict with their eating and drinking (think awkward dinner parties), develop an eating disorder, or become malnourished.

A paleo diet can compromise bone health by reducing calcium intake. A gluten-free diet can be associated with reduced fibre and vitamin intakes.

A sugar-free diet that suggests reducing fruit intake is just plain unhealthy. And sugar-free eating isn’t actually sugar-free. Many recipes contain rice malt syrup, which is chemically defined as a sugar and increases blood sugar levels much more so than an apple would.

The marketing

So, why do nutrition celebrities have so many followers when what they are selling isn’t usually evidence-based, reliable or healthy for most?

So many of us are stressed and tired, and looking for quick fixes. We associate celebrity with happiness and wealth. We’re sold a whole lifestyle and the idea that food can be a magical elixir that can cure all ails.

We are drawn in by fancy blogs, colourful cook books, Instagram feeds of stylised food photography shoots, the Twitter hashtags #paleo #cleaneating #rawfood #sugarfree #glutenfree #detox #juice, and Facebook stories of struggling lives turned around in an instant.

It’s easy to see why this is more appealing that listening to government guidelines and advice from doctors, nutritionists and dietitians that scientific evidence doesn’t support the elimination of entire food groups or elements such as dairy, gluten, legumes, grains and fruit from the diets of most people.

Perhaps we need to strategically market evidence-based nutrition information to have broader appeal.

So, turn this:

Click to enlarge

Into this:

To counter the fads, we need to consider innovative ways of communicating to Australians about what constitutes a eat a healthy, balanced diet that is based on evidence. Nutrition celebrities’ marketing strategies might teach us a thing or two about how to sell this message.

Further reading: The ‘hole’ in the pantry story: should Penguin have validated Belle Gibson’s cancer claims?

Seventeenth-century Oxford scholar Robert Burton’s lifework, The Anatomy of Melancholy, weighs in at a door-stopping 1,400 pages. But his cure for the “Black Choler” of depression came down to just six words: “Be not solitary, be not idle.” Writing today, he might add: “And maybe take a placebo.”

Placebos are sham treatments that work even though they lack an active ingredient. Pills made of sugar or corn starch have improved Parkinson’s disease, anxiety and pain. Now research suggests placebos may be as good as real drugs for treating depression.

Placebo power

In this most recent study, people with at least moderate depression received support and encouragement alone, or coupled with an antidepressant or a placebo. Those who received an antidepressant or placebo did better than those who got only support. But placebos improved depression nearly as much as the active drug and the difference wasn’t significant.

An earlier review found antidepressants offered minimal benefit over placebos except in very severe depression, where the benefit was substantial. And a 2008 study found antidepressants were no more effective even in severe depression; very depressed people were just less responsive to placebos.

One theory suggests placebos work because people expect them to. A grave doctor and austere consulting room help convince patients a drug works. Indeed, believing a dummy pill stops pain triggers endorphins in the same brain area targeted by real painkillers.

Another theory cites Pavlov’s dogs, who, after a while, just had to see the white coats of the assistants who brought their food to start drooling. This conditioning theory suggests people only need to see the pill, cream or syringe to get the intended effect, even without the active drug.

But we know active drugs cause placebo effects too. Painkillers work a lot better when a medical person says they will work. A 1998 study claimed placebo effects accounted for an estimated 75% of the effects of antidepressants.

Nonetheless, the drugs still figure prominently in Australian guidelines and in 2012-13 Australian doctors wrote 20.5 million prescriptions for antidepressants.

The right fit

But if antidepressants are little better than a placebo, why do so many people take them? Well, the placebo data have been criticised, among others, for selective analysis of studies. They may be wrong.

And there are reasons why doctors and patients might favour medication that could help even a little. A busy waiting room makes speedy prescription writing attractive; advertising could make doctors think of drugs as the first option; patients often want a “quick fix”; and our culture reinforces drugs as a natural response to illness.

A trickier question is whether doctors should even prescribe antidepressants if they are really just placebos. But placebos can be powerful and some argue we shouldn’t jeopardise their strength by telling patients. A 2008 US study of 1,200 doctors found more than half prescribe placebos, often vitamin pills.

But there may be differences between countries too. Direct-to-consumer advertising of prescription drugs, legal only in the United States and New Zealand, may influence placebo responses. Advertisements for drugs show dramatic improvements that heighten expectations. Pictures of smiling people and beautiful scenery also promote positive attitudes and beliefs.

Some think advertising is the reason placebos in antidepressant drug trials have become 14% more effective in the last 20 years.

And people with depression may show stronger placebo responses. Psychologist Irving Kirsch thinks this is because hopelessness is so dominant in depression. Placebos give hope so they may work better for this particular illness.

Limiting placebo use

Nonetheless, the American Medical Association has vetoed the use of deceptive placebos, saying they undermine trust, frustrate patient autonomy and delay proper treatment. But a 2010 study showed placebos work even if you tell the patient.

Others argue real drugs are actually superior placebos. In blinded drug trials, people who get side effects often work out they’re on the real drug and not the placebo. This makes them expect to improve, so the placebo effect kicks in.

But this too gets complicated because placebos can also cause side effects. This “nocebo” phenomenon happens when people expect bad things from a sugar pill. Maybe placebos will work better if the doctor “suggests” some side effects too?

An alternative to grappling with this often conflicting information is to raise the profile of non-drug treatments for depression. Psychotherapies such as cognitive behavioural therapy are as good as drugs, except for people with severe depression.

But adding another twist is a recent study that showed psychotherapy isn’t significantly better than a pill placebo for depression. Still, psychotherapy does provide important knowledge that promotes autonomy, a factor not measured in study comparisons.

Many active treatments are effective partly because of the placebo effect. The effect is strong in antidepressants, a fact that may need to be disclosed to patients to ensure fully informed consent. Whether sugar placebos should ever enter medical practice is another question entirely, and one that invites wide community debate.

Few discoveries have revolutionised the practice of medicine as much as the discovery of human red blood cell groups.

Unlike modern vampire and Time Lord mythologies, blood groups don’t have a particular flavour (Tru blood) or make humans susceptible to hypnotic mind control (Dr Who). Rather, blood is categorised by the naturally occurring proteins and sugars on the surface of red blood cells.

For most people, which blood group you are does not matter one jot, unless your life is at risk and you need a blood transfusion. In this case, the proteins and sugars can act as a barrier to safe transfusion of red blood cells from one person to another.

The ABO blood group system

Prior to the 20th century, early attempts at transfusing blood into humans could be unpredictable and lead to death. Looking for a solution, immunologist Karl Landsteiner found that the blood of two people could be either “compatible” or “incompatible” in a predictable way: “incompatible” blood led to “clumping” (agglutination) of red blood cells in a test tube, while “compatible blood” did not.

Along with Alfred von Decastello and Adriano Sturli, Landsteiner identified the four major blood groups: O, A, B and AB or what is known as the ABO blood group system.

Landsteiner realised what made blood types compatible or incompatible were antibodies produced against specific red blood cell sugar molecules, causing agglutination of the red cells in the test tube and destruction of the red cells in the circulation. For this work, Landsteiner was awarded the Nobel Prize in Medicine.

Ludwig Hektoen developed rigorous testing procedures of blood grouping and cross matching in 1907 which were first performed by Reuben Ottenberg. These methods have been used to reliably select the correct donor blood ever since.

Beyond the ABO blood group

In general, everyone can be classified within ABO blood group system, based on the ABO sugars. Red blood cells also contain many other proteins and sugars, known as red cell antigens. Researchers have discovered more than 300 blood group antigens, each representing different proteins on the red blood cell that perform different functions.

The importance of these red cell blood groups, however, is not necessarily what they do; you could live without several blood group antigens and be none the wiser. Their importance of lies in how they elicit an immune antibody response, and whether these new antibodies can destroy foreign red cells against which they are targeted.

The immune system of person who doesn’t have these antigens can be stimulated to make antibodies against red cell antigens that aren’t their own. This can cause red cell destruction (haemolysis) which, in its most immediate and dramatic form, can lead to severe stress to the heart and circulation, kidney failure and death. It can also lead to a delayed form of red cell destruction that occurs a week or so after a blood transfusion.

Positive or negative

One of the most important non-ABO blood groups is the Rhesus blood group system, which Landsteiner discovered in 1940 in collaboration with Alexander Weiner. This system categorises people as either positive or negative, depending on whether they have Rhesus D antigen on their red cells (O- or O+ for example).

Since the late 1800s, physicians had noted that following a successful first pregnancy, some mothers could lose their subsequent babies through a disease called haemolytic disease of the fetus and newborn. For the majority of babies, this condition was attributable to the Rhesus D antigen.

Researchers realised that Rhesus D-negative mothers were exposed to Rhesus D antigen through the course of their pregnancy. The baby had inherited this red cell antigen from their father. The mother’s immune system therefore reacted against this foreign red cell antigen by producing antibodies which could cross the placenta and destroy the red cells of the baby in subsequent pregnancies.

The understanding of the Rhesus system led to strategies that have dramatically reduced haemolytic disease among newborns. Rhesus D-negative women of child-bearing age are only given blood transfusions of Rhesus D-negative blood to prevent stimulating the immune system against this antigen.

Pregnant Rhesus D-negative women are also given special anti-D immunoglobulin during their pregnancy, after delivery and following any trauma or pregnancy-related procedure. Again, this helps prevent foreign Rhesus D-positive red cells from stimulating the mother’s immune system.

Rare blood groups

What ultimately determines our blood group is our genetics: our parents, our ancestors and also their migration patterns.

Rare blood groups arise from inheritable mutations of red blood cell genes in different populations. This can make it very difficult to find correctly “matched” blood donor units for people with rare blood groups simply because they are uncommon in the usual volunteer blood donor population.

The red cell blood group Kidd(null) phenotype (Jka-b-) which is more common in Finnish and Polynesian populations, for instance, is very rare in Australian blood donors. Unless a correctly matched Jka-b- blood is found, there is a risk of developing a haemolytic transfusion reaction or haemolytic disease of the newborn, as patients develop antibodies that are acquired to Kidd red cell blood groups on the transfused blood.

People with the Bombay red cell phenotype have only a one in a million chance of finding a suitable blood donor. In this setting, transfusion may be sought from a family member, who is much more likely to have the correct blood phenotype.

It’s likely that you or someone you know will require a blood transfusion at some stage in life. One of the simplest things we can do as individuals is to become a volunteer blood donor.

Gluten is a protein found in the grains wheat, rye and barley. For people with the autoimmune condition coeliac disease, eating foods that contain gluten can damage the lining of the intestines. Over time, this damage can lead to nutritional deficiencies, osteoporosis and cancer.

Coeliac disease affects 1% of Australians, though only one in five of those may know they have it. The only way to diagnose coeliac disease is to have a positive intestinal biopsy. People with coeliac disease must follow a gluten-free diet; there is currently no other treatment.

But others are also choosing to go gluten-free. According to the latest National Health Survey, 2.5% of Australians aged two or over reported avoiding gluten (about 544,000 people). This means that 1.5% or 326,000 people may be unnecessarily avoiding gluten.

So, is a gluten-free diet warranted by anyone but people with coeliac disease?

The alternative medicine crowd would have you believe gluten- and grain-based foods cause a host of nasties from dementia to cancer. Others tout gluten-free diets as a helpful weight-loss tool. And the grain-avoiding paleo philosophy rules the lives of some vocal, yet otherwise sensible, Australians.

It’s no wonder some people are questioning their gluten intake. But rest assured, there is no credible evidence grain-based foods cause disease. Nor is there any evidence gluten-free diets aid weight loss, though there is strong evidence to the contrary.

While it’s certainly helpful for long-term health to reduce processed foods, grains form the staple foods of many societies and provide key nutrients. The Australian Guide to Healthy Eating encourages a variety of grain-based foods precisely because these foods make achieving nutritional adequacy more straightforward and are culturally appropriate for the majority of Australians.

Gluten sensitivity

For some people, reducing wheat can help reduce uncomfortable gastrointestinal symptoms.

Wheat also contains fructans, a form of fibre which is rapidly fermented by bowel bacteria. This can lead to flatulence and discomfort in some people.

Many irritable bowel syndrome (IBS) sufferers have achieved good symptom control following a low FODMAP diet, which restricts a number of carbohydrates (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) which can be poorly absorbed in the small intestine. Fructans are one such carbohydrate.

Non-coeliac gluten sensitivity is a fall-back diagnosis if symptoms are not relieved with a low fodmap diet.

But a recent small but clever study now disputes the diagnosis all together. All the food for the study participants was provided and the diets were controlled for gluten, FODMAPs, and food chemical components known to elicit responses in food sensitive people (such as salicylates, amines and glutamates).

Many participants reported symptoms, but they weren’t being caused by gluten. There is clearly more work to be done here but it looks like gluten has been unfairly accused.

A word of warning to young women

People who avoid gluten without a medical reason and without individualised dietetic advice are at risk of nutrient inadequacies, especially if an unplanned pregnancy occurs.

Even with expert advice from a dietitian, people with coeliac disease do not easily achieve nutrient adequacy. A recent study of the gluten-free diets of new and experienced coeliacs found that significant numbers of adult female participants did not achieve the recommended dietary intakes (RDI) or even the population averages of thiamin, folate, calcium, iron or fibre. The most concerning of these nutrients is folate.

Australian women of child bearing age have the highest prevalence of gluten avoidance: 5% of 19- to 30-year-olds and 4.8% of 31- to 50-year-olds. This is not surprising, given women are more likely to suffer from IBS and also more likely to diet with the intention of weight control.

Folic acid (folate) has been added to wheat flour in Australia as a public health measure since 2009 to help prevent neural tube defects such as spina bifida in babies. Fortification of the food supply is particularly helpful given that up to 50% of pregnancies are unplanned and folate should be consumed for at least a month before conception.

But gluten-free breads are not routinely fortified with folate and gluten-free grains and vegetable starches are not rich sources, leaving those following a gluten-free lifestyle without a folate safety net.

What about the health claims?

Gluten-free foods may be found in the health food aisle of the supermarket, but the reality is gluten-free food manufacturers chase dollars, not health. In the rush to meet consumer demand, many food manufacturers have prioritised meeting gluten-free criteria and palatability over true substitution for gluten.

Foods that are naturally gluten free are now even being labelled gluten-free in order to capitalise on this growing market.

To be truly helpful for their consumers, manufacturers need to take measures to keep their products nutrient-rich, not just gluten free.

Regardless of whether the reason to follow a gluten-free diet is medical or philosophical, it’s important to focus on achieving adequate nourishment. A nutritionally adequate gluten-free diet needs to be well planned and well executed. It’s not simply a matter of cutting out grains and choosing labels which say “gluten free”.

If you’re an adult and have ever visited a doctor, you’ve probably had your blood pressure measured. General practitioners tend to obsess over blood pressure. But with good reason: hypertension, or persistently high blood pressure, can lead to heart disease, stroke and diabetes, the nation’s biggest killers.

What is blood pressure?

Blood pressure refers to how hard the blood is pushing against the wall of arteries – these can be thought of as the pipes that deliver blood from the heart (the blood “pump”) to the rest of the body.

This pressure is necessary for the blood to flow. Using a plumbing analogy, imagine the effect of a drop in water pressure to water flow from the garden hose.

Blood pressure naturally varies throughout the day depending on posture, activity and stress. It can also be elevated or lowered as a consequence of illness or disease.

Stephen Hales, an 18th-century English clergyman and scientist, first measured the blood pressure of animals in a series of experiments that involved inserting tubes into their arteries. In one experiment with a horse, he describes the blood rising to eight feet in height in the tube!

Blood pressure measurement would almost certainly be unpopular if it involved inserting long glass tubes into people. Happily, Italian physician Scipione Riva-Rocci developed the conventional sphygmomanometer, or blood pressure meter, in 1896.

Soon afterwards, Russian physician Nikolai Korotkoff discovered the sounds that can be heard with a stethoscope over the inner elbow while using a sphygmomanometer. His technique remains the standard method for measuring blood pressure today.

Interestingly, the conventional sphygmomanometer uses a column of liquid mercury to indicate the pressure. As mercury is so much denser than water or blood, even very elevated blood pressures result in it rising no more than about a foot.

This quirk of medical history gives us the modern measurement unit for blood pressure: millimetres of mercury (mmHg). A blood pressure measurement of 140 mmHg literally means that the pressure will push up a column of liquid mercury 14 centimetres.

Two numbers are given when reporting blood pressures, such as 140/90 mmHg. The first number is the systolic blood pressure. This is the pressure when the heart is contracting to pump its content of blood into the circulation.

The second number is the diastolic blood pressure. This is the pressure when the heart is relaxing and is refilling with blood.

What is normal?

The National Heart Foundation guidelines define “normal” blood pressure withing the following range:

• Systolic blood pressure: 100 to 139 mmHg
• Diastolic blood pressure: 60 to 89 mmHg.

These thresholds are arbitrary, but a blood pressure less than 140/90 mmHg is not labelled as high.

We’re also moving away from categorical descriptions of hypertension, based on blood pressure reading alone, towards a model where blood pressure is considered alongside other risk factors to determine whether drug or lifestyle interventions are needed.

Clinicians now calculate the patent’s absolute cardiovascular disease risk: the probability they will have a heart attack or stroke in the short and medium term, which includes age and cholesterol levels. This calculator can help you work out your absolute disease risk.

All adults should consider having their blood pressure measured at least once every two years. If it’s elevated, and confirmed, you’ll work with your GP to create a management plan to lower your blood pressure. This is likely to lifestyle changes such as:

• getting regular physical activity
• quitting smoking
• reducing the amount of salt you eat
• increasing the amount of potassium you consume (from foods such as parsley, dried apricots, some nuts, bamboo shoots, bananas, avocados, soybeans and bran)
• losing weight
• drinking less alcohol.

Keep in mind that visiting the doctor can provoke anxiety, so the blood pressure can be elevated in response to the testing procedure itself. This has been called the “white coat effect”.

If this is suspected, your GP might try recording your blood pressure over a number of visits, or use ambulatory or home blood pressure monitoring to get an accurate reading.

This article was co-authored by Dr Patrick Khoury, a GP registrar at the General Practice Unit, Fairfield Hospital.