Author: Dan Baumgardt, Senior Lecturer, School of Physiology, Pharmacology and Neuroscience, University of Bristol

Does anyone else think we’ve all become a bit too protein-obsessed? Once upon a time, we got our protein from meat, fish, dairy and pulses. Now it seems like every consumable product comes loaded with it — from energy bars to protein-packed cereals and baked goods.

I’m surprised no one’s thought of stirring it into their tea for a boost. Oh wait, they have.

That’s not to say I’m anti-protein. Far from it. Protein plays an essential role in body functions such as growth, immunity and digestion. It’s important that we get enough of it each day.

But the million-dollar questions we should be asking are: how much do we actually need? When is it too much, or too little? And where should we be getting it from?

Protein is one of the three macronutrients we need in the largest amounts – the others being carbohydrates and fats. Micronutrients such as vitamins and minerals are important too, but they’re needed in much smaller quantities — typically milligrams, or even micrograms.

Protein is involved in a huge range of physiological processes. It’s of course crucial for muscle growth and repair. Bodybuilders looking for an Adonis (or Amazonian) physique often consume large amounts alongside strength training. But protein isn’t just about muscles – it’s a core structural material for bone, skin, hair and nails too.

It also plays vital roles inside the body. It allows muscles to contract, makes up digestive and metabolic enzymes, and is a key component of haemoglobin (which carries oxygen), ferritin (which stores iron) and antibodies (which fight infection).

But remember: protein doesn’t work in isolation. Our bodies also rely on carbohydrates and fats — providing short and long-term energy sources that are just as important.

Carbohydrates provide four calories of energy per gram, and fats proide nine calories per gram. While protein can also be used as an energy source – also producing four calories per gram – carbs are more accessible for tissues to use rapidly. And crucially, building muscle also requires fuel. So, if your diet is too low in carbohydrates, your muscle gains may stall and you may find yourself depleted of energy.

In general, protein is filling and can help reduce snacking. And too little protein can be harmful. Protein deficiency can occur due to inadequate diet, eating disorders, or conditions such as cancer, Crohn’s, or liver disease. Symptoms include fatigue, muscle wasting and a weakened immune system.

Because protein also helps regulate fluid balance in the body, a deficiency can lead to swelling or oedema. In severe cases, as seen in some developing countries, the condition kwashiorkor — marked by a swollen belly — can result from inadequate protein intake.

How much?

It can sometimes be difficult to work out how much protein you should be eating each day, especially when different sources give variable advice.

A good starting point is to consider your overall energy requirements. Government recommendations suggest that up to 35% of your daily calories should come from fat, and up to 50% from carbohydrates. That leaves a minimum of 15% for protein — which for someone on a 2,500-calorie diet works out to about 95g of protein per day.

Another calculation accounts for your body size too, giving a value more specific to the individual. Around 0.8g protein per kilogram of body weight for a sedentary adult is advised.

For athletes and bodybuilders – who often aim for around 2g per kilogram — this can mean as much as 200g of protein a day. And that’s hard to achieve through regular food alone. For context, 30 eggs contain 200g of protein, as does 2.5kg of cooked beans. Certain foods have more protein (like the go-to chicken breast), though the overall volume of food required can still be high.

That’s where protein powder often comes in — usually offering 20g–30g of protein per scoop – as supplementation. It’s absolutely fine to incorporate some powder or shakes into a healthy diet alongside wholefoods, which are the best protein sources. But it’s important to set limits – and avoid the temptation to go overboard.

Too much

Is it possible to be taking on too much protein? The answer is yes, if you’re regularly consuming more than your body needs.

Excess protein is broken down and excreted through the kidneys, which may cause dehydration and place additional strain on renal function. Unused protein can also be converted into fat, potentially leading to weight gain. High-protein diets are sometimes associated with gastrointestinal side effects such as bloating, diarrhoea and bad breath.

And while many high-protein foods are healthier, others (such as red or processed meats) may also be high in saturated fat, which can increase the risk of serious conditions like heart disease.

So yes — protein is essential, but balance is key. Your daily needs depend on your body size, activity levels and general health. Consider your goals: are you aiming to maintain a certain weight, or looking to lose fat or gain muscle? Some starting points are:

• aim for at least 0.8g protein per kilogram of body mass daily
• balance it with adequate carbs and fats
• prioritise wholefood sources over protein supplements where possible
• increase your intake responsibly if you’re training hard or trying to gain muscle
• but be cautious with too high, sustained intakes — these may do more harm than good.

As someone who could do with a wee bit more in his own diet, I’m off to try that protein-in-my-tea trick. Wish me luck.

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When the COVID pandemic hit, many people turned to the eerily prescient film Contagion (2011) for answers – or at least for catharsis. Suddenly, its hypothetical plot felt all too real. Applauded for its scientific accuracy, the film offered more than suspense – it offered lessons.

One scene in particular stands out. Kate Winslet’s character delivers a concise lesson on the infectious power of various pathogens – explaining how they can be spread from our hands to the many objects we encounter each day – “door knobs, water fountains, elevator buttons and each other”. These everyday objects, known as fomites, can become silent vehicles for infection.

She also considered how each infection is given a value called R0 (or R-nought) based on how many other people are likely to become infected from another. So, for an R0 of two, each infected patient will spread the disease to two others. Who will collectively then give it to four more. And so a breakout unfolds.

The R0 measure indicates how an infection will spread in a population. If it’s greater than one (as seen above), the outcome is disease spread. An R0 of one means the level of people being infected will remain stable, and if it’s less than one, the disease will often die out with time.

Circulating infections spread through a variety of routes and differ widely in how contagious they are. Some are transmitted via droplets or aerosols – such as those released through coughing or sneezing – while others spread through blood, insects (like ticks and mosquitoes), or contaminated food and water.

But if we step back to think about how we can protect ourselves from developing an infectious disease, one important lesson is in understanding how they spread. And as we’ll see, it’s also a lesson in protecting others, not just ourselves. Here is a rundown of some of the most and least infectious diseases on the planet.

In first place for most contagious is measles.

Measles has made a resurgence globally in recent years, including in high-income countries like the UK and US. While several factors contribute to this trend, the primary cause is a decline in childhood vaccination rates. This drop has been driven by disruptions such as the COVID pandemic and global conflict, as well as the spread of misinformation about vaccine safety.

The R0 number for measles is between 12 and 18. If you do the maths, two cycles of transmission from that first infected person could lead to 342 people catching the illness. That’s a staggering number from just one patient – but luckily, the protective power of vaccination helps reduce the actual spread by lowering the number of people susceptible to infection.

Measles is extraordinarily virulent, spreading through tiny airborne particles released during coughing or sneezing. It doesn’t even require direct contact. It’s so infectious that an unvaccinated person can catch the virus just by entering a room where an infected person was present two hours earlier.

People can also be infectious and spread the virus before they develop symptoms or have any reason to isolate.

Other infectious diseases with high R0 values include pertussis, or whooping cough (12 to 17), chickenpox (ten to 12), and COVID, which varies by subtype but generally falls between eight and 12. While many patients recover fully from these conditions, they can still lead to serious complications, including pneumonia, seizures, meningitis, blindness, and, in some cases, death.

Low spread, high stakes

At the other end of the spectrum, a lower infectivity rate doesn’t mean a disease is any less dangerous.

Take tuberculosis (TB), for example, which has an R0 ranging from less than one up to four. This range varies depending on local factors like living conditions and the quality of available healthcare.

Caused by the bacterium] Mycobacterium tuberculosis, TB is also airborne but spreads more slowly, usually requiring prolonged close contact with someone with the active disease. Outbreaks tend to occur among people who share living spaces – such as families, households, and in shelters or prisons.

The real danger with TB lies in how difficult it is to treat. Once established, it requires a combination of four antibiotics taken over a minimum of six months. Standard antibiotics like penicillin are ineffective, and the infection can spread beyond the lungs to other parts of the body, including the brain, bones, liver and joints.

What’s more, cases of drug-resistant TB are on the rise, where the bacteria no longer respond to one or more of the antibiotics used in treatment.

Other diseases with lower infectivity include Ebola – which is highly fatal but spreads through close physical contact with bodily fluids. Its R0 ranges from 1.5 to 2.5.

Diseases with the lowest R0 values – below one – include Middle East respiratory syndrome (Mers), bird flu and leprosy. While these infections are less contagious, their severity and potential complications should not be underestimated.

The threat posed by any infectious disease depends not only on how it affects the body, but also on how easily it spreads. Preventative measures like immunisation play a vital role – not just in protecting people, but also in limiting transmission to those who cannot receive some vaccinations – such as infants, pregnant women and people with severe allergies or weakened immune systems. These individuals are also more vulnerable to infection in general.

This is where herd immunity becomes essential. By achieving widespread immunity within the population, we help protect people who are most susceptible.

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Summer is synonymous with adventure, with millions flocking to exotic destinations to experience different cultures, cuisines and landscapes. But what happens when the souvenir you bring back isn’t a fridge magnet or a tea towel, but a new illness?

International travel poses a risk of catching something more than a run-of-the-mill bug, so it’s important to be vigilant for the telltale symptoms. Here are the main ones to look out for while away and when you return.

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Fever

Fever is a common symptom to note after international travel – especially to tropical or subtropical regions. While a feature of many different illnesses, it can be the first sign of an infection – sometimes a serious one.

One of the most well-known travel-related illnesses linked to fever is malaria. Spread by mosquito bites in endemic regions, malaria is a protozoal infection that often begins with flu-like symptoms, such as headache and muscle aches, progressing to severe fever, sweating and shaking chills.

Other signs can include jaundice (yellowing of the skin or eyes), swollen lymph nodes, rashes and abdominal pain – though symptoms vary widely and can mimic many other illnesses.

Prompt medical attention is essential. Malaria is serious and can become life threatening. It’s also worth noting that symptoms may not appear until weeks or even months after returning home. In the UK, there are around 2,000 imported malaria cases each year.

Travellers to at-risk areas are strongly advised to take preventative measures. This includes mosquito-bite avoidance as well as prescribed antimalarial medications, such as Malarone and doxycycline. Although these drugs aren’t 100% effective, they significantly reduce the risk of infection.

Aside from malaria, other mosquito-borne diseases can cause fever. Dengue fever, a viral infection found in tropical and subtropical regions, leads to symptoms including high temperatures, intense headaches, body aches and rashes, which overlap with both malaria and other common viral illnesses.

Most people recover with rest, fluids and paracetamol, but in some instances, dengue can become severe and requires emergency hospital treatment. A vaccine is also available – but is only recommended for people who have had dengue before, as it provides good protection in this group.

Any fever after international travel should be taken seriously. Don’t brush it off as something you’ve just picked up on the plane – please see a doctor. A simple test could lead to early diagnosis and might save your life.

Diarrhoea

Few travel-related issues are as common – or as unwelcome – as diarrhoea. It’s estimated that up to six in ten travellers will experience at least one episode during or shortly after their trip. For some, it’s an unpleasant disruption mid-holiday; for others, symptoms emerge once they’re back home.

Traveller’s diarrhoea is typically caused by eating food or drinking water containing certain microbes (bacteria, viruses, parasites) or their toxins. Identifying the more serious culprits early is essential – especially when symptoms go beyond mild discomfort.

Warning signs to look out for include large volumes of watery diarrhoea, visible blood in the stool or explosive bowel movements. These may suggest a more serious infection, such as giardia, cholera or amoebic dysentery.

These conditions are more common in regions with poor sanitation and are especially prevalent in parts of the tropics.

Some infections may require targeted antibiotics or antiparasitic treatment. But regardless of the cause, the biggest immediate risk with any severe diarrhoea is dehydration from copious fluid loss. In serious cases, hospital admission for intravenous fluids may be necessary.

The key message for returning travellers: if diarrhoea is severe, persistent or accompanied by worrying symptoms, see a doctor. What starts as a nuisance could quickly escalate without the right care.

And if you have blood in your stool, make sure you seek medical advice.

Jaundice

If you’ve returned from a trip with a change in skin tone, it may not just be a suntan. A yellowish tint to the skin – or more noticeably, the whites of the eyes – could be a sign of jaundice, another finding that warrants medical attention.

Jaundice is not a disease itself, but a visible sign that something may be wrong with either the liver or blood. It results from a buildup of bilirubin, a yellow pigment that forms when red blood cells break down, and which is then processed by the liver.

Several travel-related illnesses can cause jaundice. Malaria is one culprit as is the mosquito-borne yellow fever. But another common cause is hepatitis – inflammation of the liver.

Viral hepatitis comes in several forms. Hepatitis A and E are spread via contaminated food or water – common in areas with poor sanitation. In contrast, hepatitis B and C are blood-borne, transmitted through intravenous drug use, contaminated medical equipment or unprotected sex.

Besides jaundice, hepatitis can cause a range of symptoms, including fever, nausea, fatigue, vomiting and abdominal discomfort. A diagnosis typically requires blood tests, both to confirm hepatitis and to rule out other causes. While many instances of hepatitis are viral, not all are, and treatment depends on the underlying cause.

As we’ve seen, a variety of unpleasant medical conditions can affect the unlucky traveller. But we’ve also seen that the associated symptoms are rather non-specific. Indeed, some can be caused by conditions that are short-lived and require only rest and recuperation to get over a rough few days. But the area between them is decidedly grey.

So plan your trip carefully, be wary of high-risk activities while abroad – such as taking drugs or having unprotected sex – and stay alert to symptoms that develop during or after travel. If you feel unwell, don’t ignore it. Seek medical attention promptly to identify the cause and begin appropriate treatment.