A factual foundation for the debate is provided by a review of the eating patterns of early humans and how we adapted to digest starches softened by cooking. The researchers contend that it was digestible starches that provided extra energy needed to fuel the energy needs of bigger brains, rather than extra protein from meat to grow these brains.

But the most striking thing about human diets is just how variable they have been and the adaptations that have taken place. Furthermore, the American evolutionary biologist Marlene Zuk in her book Paleofantasy contends that these dietary adaptations are not fixed on what our ancestors ate in caves at some time in the past.

So are our energy, or protein, needs much different from other mammals of similar size? Brains demand a lot of energy but so does the liver and the digestive tract. The extra nutrition that we need for brain work may be counterbalanced, at least partially, by a lesser need for:

• a long gut to process poor quality foods, or
• a large liver to handle nasty chemicals in these plant parts.

Once built, a large brain does not require extra sources of protein to maintain its activities.

My studies on the dietary requirements of savanna-inhabiting herbivores highlight how these animals must cope with the dry season when most herbage is brown and indigestible even with the aid of microbial symbionts in the gut.

But carnivores do not have this problem because the dry season is when weakened herbivores are most readily killed, especially when they concentrate around scarce waterholes.

The role of carbs among early humans

Meat has long been part of human diets, along with carbohydrates provided by fruits, tubers and grains. We can get by without it, obtaining protein from milk or, with some planning, from legumes.

The early humans that consumed most meat were the Neanderthals, who lived in Europe many thousand years ago, but were not our ancestors. Meat formed the crucial lean-season food for the Neanderthal people during successive winters when plants were seasonally buried under deep snow, but later also for the modern humans who spread through Eurasia and displaced them around 40 000 years ago.

Unlike tropical Africa, meat could be stored during the freezing winters of the far north to provide a reliable food source, especially in the form of large carcasses of elephant-like proboscideans.

This led to a wave of large mammal extinctions as humans spread rapidly into Australia and entered the Americas towards the end of the last Ice Age. By that time hunting technology had been honed and meat routinely supplemented plant food, but the latter remained the dietary staple for African hunter-gatherers like the Bushmen or San people into modern times.

The food journey within evolution

Coping with the intensifying dry season in the expanding African savanna was a critical issue for human ancestors during the evolutionary transition from ape-men to the first humans between three and two million years ago. How did our ape-men ancestors gather sufficient to eat during this time of the year when nutritious fruits and leaves were scarce?

This was when meat, or at least the marrow left within bones, could have become a nutritional fallback, probably acquired by scavenging from animal carcasses not completely consumed by big fierce carnivores, along with underground storage organs of plants.

Obtaining this meat required more walking and hence longer limbs, hands freed to carry, security in numbers and stone weapons to throw at threatening carnivore fangs, but not much expansion in cranial capacity. These were features of the early Australopithicines.

At this early time, another branch of ape-men, placed in the genus Paranthropus, took a different adaptive route. They developed huge jaws to chew on tough plant foods extracted from underground storage organs to get them through the dry season.

The last representative of this genus faded out nearly a million years ago when this strategy eventually became unviable. About that time the lineage leading to early humans discovered cooking, or at least how to use it effectively to make starches stored by plants more readily digestible, according to the article in The Quarterly Review of Biology.

Adding this reliably found source of energy to the proteins acquired more opportunistically by hunting animals or gathering shellfish provided the means to survive through seasonal bottlenecks in food availability and build even bigger brains and the adaptations that followed.

A supporting adaptation was to store more body fat to get through the lean periods, especially among women supporting dependent offspring. This works against us now that foods supplying carbohydrates are plentiful.

The modern day dilemma

The problems we currently face are that we retain a craving for sugar, which was scarce the past, while most of the starchy carbohydrates we eat are highly refined. This means losing out on the other nutrients in plant parts like minerals and vitamins, and most basically fibre.

A meat-based diet could have a role to play for people who have a propensity to store fat by filling the gut for longer and alleviating desires to snack on sweets between meals. More important generally is the need to exercise so that we are hungry enough to consume sufficient food to provide the scarce micronutrients that we also require for healthy bodies.

The best advice is to eat lots of things: meat if you can afford it and justify its planetary costs to produce, but also all kinds of good food, as least refined and processed as you can obtain (apart from wines).

We’ve known for some time that our eyes move around during the dreaming phase of sleep, much like when we’re awake and looking at a visual scene. The phase of sleep is called rapid eye movement sleep, or REM sleep.

New research, published today in the journal Nature Communications, shows brain activity during the dreaming phase of sleep is remarkably similar to brain activity when we’re awake and processing new visual images, suggesting the brain “sees” dreams.

While researchers have suspected this may be the case, it’s the first time investigators have been able to record brain activity from within the brain.

A quick history of dream research

Dreams and their purpose have been one of the enduring mysteries of sleep. Early dream theorists, such as Sigmund Freud, argued that the function of dreaming was to preserve sleep by expressing unfulfilled desires or wishes in the unconscious state.

More recently, researchers have investigated the function and processes of sleep and dreams by measuring the physiological signals that characterise this state of consciousness.

Just over 60 years ago, American sleep researcher Eugene Aserinsky stumbled across rapid eye movements during sleep almost accidentally, during an overnight sleep study recording of his eight-year-old son. His seminal 1953 paper reported “rapid, jerky and binocularly symmetrical” eye movements during periods of sleep.

These eye movements were also associated with increased brain activity, thus discounting the idea that sleep is a completely passive phenomenon. During REM sleep, our brains are active and behave similarly to wakefulness or light sleep. But muscle activity is suppressed so we can’t physically carry out our dreams.

In a pioneering 1957 paper, American researchers William Dement and Nathaniel Kleitman examined the relationship between eye movements and dream content. They woke participants during REM sleep and asked them to describe their dream. The researchers then looked at how their dream description related to the type of eye movements they were experiencing at the time (vertical, horizontal, or a mix of both).

Participants who were woken after a series of vertical movements reported “climbing up a ladder”, and “standing at the bottom of the cliff operating a hoist and looking up at climbers”, whereas one participant who was woken after horizontal eye movements reported dreaming about “two people throwing tomatoes at each other”. In contrast, those who had mixed eye movements tended to be watching people close to them with no description of distance or vertical vision.

Since this study, the evidence for this association between the REMs and dream content is not consistent. Individuals who have been blind from birth, for instance, have REMs but no visual dream content.

But in support of Dement’s finding, a recent study in patients with REM behaviour disorder (where people act out their dreams due to a lack of muscle paralysis), found a strong association between goal-oriented limb and head action and eye gaze direction during REM sleep.

Brain activity during sleep

In everyday life, when we see things, our eyes and brain behave in characteristic ways to gather and process the information in our visual field and give it meaning. But the function of eye movements during sleep and dreaming are relatively unknown. Today’s Nature Communication paper provides some insights.

Usually, brain activity is measured non-invasively from the scalp. But the investigators, from Tel Aviv University, recorded the activity of the brain, from within the brain, in patients with epilepsy.

Patients whose epilepsy cannot be controlled with medication have electrodes surgically placed within the brain as a clinical means to map their epileptic activity, and assess suitability for surgery as a treatment. These electrodes were implanted in the medial temporal lobe – a region that is associated with visual awareness.

Researchers compared brain activity of these patients across three settings: REM sleep brain activity, wakeful eye movements in darkness (no visual processing) and wakeful fixed-gaze visual processing (no eye movements). They wanted to test whether brain behaviour during sleep was more closely related to physical movement, or the processing of visual information.

Results showed that during rapid eye movements in sleep, the brain activity was more closely related to the brain activity during visual processing during wakefulness (without movement) than physical movements of the eyes in darkness where no visual processing was taking place.

These results suggest that the rapid eye movements that occur in sleep are linked to visual processing rather than just physical activation or movement. So, the participants may have actually been looking at a dream image, rather than these eye movements simply reflecting motor discharge in the brain.

While much remains unknown, this detailed processing of our dream images suggests that rapid eye movements may actually modulate our brain activity during sleep. We know that sleep is needed for rest and rejuvenation, but it’s likely to have other important functions as well.

In line with the earliest of theories about why we dream, are we processing content that has been consciously or unconsciously avoided during wakefulness, but somehow “needs” to be dealt with at least during sleep to maintain our psychological well-being?

Are the eye movements a simple byproduct of the visual processing that occurs of the images we dream?

Is there a psychological basis to why we need to process these images during sleep, and does this lend to better psychological outcomes in a similar way to sleep aiding physical functioning?

These and many questions drive the ongoing research into why we sleep, and what its precise benefits are.

While excess weight and obesity is a growing global concern, there has been more and more advertising and promotional effort encouraging the consumption of unhealthy food.

In many cases this marketing is targeted at children, and takes place online. In our recent study we investigated the impact of online marketing communications on children and their intention to consume unhealthy food. We found fast food ads on social networking sites can manipulate young audiences – their purchasing likelihood, their views of fast food and their eating habits.

The qualitative study included a sample of 40 Australian children who use social networking sites. Half (21) of the children were male and the average age was 14 (the youngest being 12 and the oldest 16). Their parents were also present during the interview, however they agreed not to intervene during the conversation.

A growing problem

The prevalence of excess weight and obesity among Australians has been growing for the past 30 years. Between 2011 and 2012, around 60% of Australian adults were classified as overweight, and more than 25% of these fell into the obese category. In 2013, more than 12 million, or three in five Australian adults, were overweight or obese. On top of that, one in four Australian children were overweight or obese. Excess weight and obesity is only beaten by smoking and high blood pressure as a contributor to a burden of diseases.

Despite this, the food industry is succeeding in using marketing communications to change attitudes, perceptions and perceived norms associated with unhealthy food.

Consumers are lured by surprisingly cheap deals, which are especially attractive to teenagers and young adults with low income. But sales promotions such as discounts and coupons often offer only short-term benefits to consumers and are usually not effective among middle-age adults.

However, if a promotion is offered for a long period of time (i.e. more than three months), it can actually influence customer habits, encouraging repeat purchases – for example, the $1 frozen Coke.

Similarly, sales promotions can make other brands be perceived as less attractive by customers after a period of time. For instance, the $1 frozen Coke campaigns by McDonald’s and Hungry Jack’s affect the perception of frozen Coke in terms of monetary value. Many consumers become less willing to buy a frozen Coke that is more expensive than $1. The same can be said of $2 burgers or $5 pizzas.

The role of social networks

More than half (16 out of 30) of the respondents admitted they tended to change their eating habits after repeatedly being exposed to advertisements on social networking sites.

“Yes, many people say that it is not good to eat fast food. I used to think so but not anymore. Look at their ads, they are colourful, many options and cheap.”

“I just cannot resist it… I had been looking at the ads day after day and I decided that I needed to try these”.

Interestingly, fast food was associated with socialisation and fun among young consumers.

“The ads make me feel like this is where we belong to. This is our lifestyle…where we hang out and can be ourselves.”

“This is about our culture, young, active and free. We are kids but also not kids. We are different.”

Peer pressure

Peer pressure is heavily related to eating habits, especially during puberty when there is usually a shift from home influence to group motivation. Teenagers and young adults in particular tend to choose a particular type of food under peer pressure.

More than 70% of teenagers will choose a food according to the preference of their friends. This means marketing communications promoting fast food consumption can create a snowball effect within this group of customers. For example, Jack, Sara and Park go out together. If Jack and Sara order Big Burgers with extra cheese, the likelihood that Park will order another Big Burger with extra cheese is approximately 75%. In contrast, only 2.7% of people aged over 40 choose fast food because of their peers.

It’s clear marketing efforts by fast food chains can promote unhealthy eating habits. Also, peer influence plays an important part in forming eating habits. This means the intervention of government and health organisations should concentrate on increasing customers’ attention to health issues, self-efficacy and perceived norms, and at the same time, lessening the influence of marketing efforts aimed at motivating unhealthy eating habits.