Circannual Nutrition:  The Natural Seasonal Cycle of Carbs & Fat Revealed

Have you ever wondered how bears, and every other animal in nature, manage to gain fat to survive the impending winter and effortlessly lean out again in spring?  

They’re not counting their macros in MyFitnessPal to intentionally bulk and cut. 

Instead, they’re responding to the changes in their environment that oscillate with the seasons. 

In autumn, when winter is coming, they eat more of the tastier food available to bulk up.  Then, when winter is over, they naturally lose the winter blubber. 

In this article, we dive into the data from 155,676 days of data from our Optimisers over the past six years to understand the circannual variation in our nutrition patterns that align with eating less vs eating more. 

As you will see, modern humans have a lot in common with hibernating bears.  But our modern food system has nudged us towards a perpetual autumn. 

Empowered with a deeper understanding of your biology, you can hack your food choices to manage your appetite naturally. 

Beadnose the bear in spring and autumn.

Highlights

  • Our energy intake has a small peak in spring around Easter and a larger peak in autumn around Halloween, Thanksgiving, and Christmas in the US. 
  • These modern celebrations have their roots in harvest celebrations. 
  • Protein remains stable across the year.  Meanwhile, carbs rise in spring/summer and drop in autumn.  Conversely, our fat intake peaks in autumn with a low in summer.
  • Modern food processing has given us access to ultra-processed food that aligns with the autumnal combination of fat and carbs. 
  • The tasty combination of fat and carbs signals to our bodies that winter is coming, and we need to eat more of these delicious foods.
  • Reducing carbs and/or fat while prioritising protein empowers us to hack our biology, increase satiety and lower our appetite to move away from fattening autumnal foods.   

Understanding Circannual Nutrition

Circannual nutrition has fascinated me since 2017 when I first read Cian Foley’s Don’t Eat for Winter

Foley’s central premise is that nature follows a yearly cycle, with more carbs available in summer.   Autumn is a magical time when fat and carbohydrates come together.  These foods hit our bliss points and overdrive our dopamine circuits, ensuring we eat more to store fat and survive the impending winter. 

In pre-agricultural times, it was often a close shave.  Thankfully, Mother Nature rescued us from winter starvation by providing autumnal foods that ensured we built fat to survive when food was about to become scarce. 

Happily, we made it through to spring, when there is plenty of lean protein and fresh green shoots to nourish us again, and the cycle repeats. 

People who didn’t follow this pattern didn’t survive winter, so they didn’t become our ancestors.  These cravings for autumnal fat and carb combo foods are likely hard-coded into our modern biology.

This is about more than seasonal eating in our modern world.  Understanding how our environment impacts our appetite empowers us to make better food choices and proactively take control of our appetite. 

The Fundamental ‘Problem’ With Modern Food

Our modern food environment creates a mismatch between our biology, nature, and processed foods.  

It’s not that we lack willpower or that specific foods are inherently bad.  The problem is the disruption of natural nutritional cycles caused by the year-round availability of fat—and carb-rich foods.  

Humans have always found ingenious ways to obtain the energy and nutrients they need to survive and thrive.  However, in recent times, our technology and creativity have enabled us to produce abundant quantities of fat-and-carb autumnal signature foods year-round. 

These foods taste great and yield high-profit margins for big food companies, but they are not good for our health or waistlines.

Evolution of Our Food System

As we can see in the chart below, a century ago, Americans got most of their energy from carbs, with only about 30% coming from fat.  

This carb-heavy dietary pattern is a summer-like nutritional setting. However, as our modern food system has become more processed, the proportion of carbs and fat in the US food system has drifted together as more refined fats have been added.  

Note:  I’m not saying that fat is bad and carbs are good.  If we had data from people living closer to the North Pole, we’d likely see a fat-rich diet with minimal carbs drifting towards a similar blend of fat and carbs. 

The chart below shows how the macros in the US have changed over the past century, leading to a rapid spike in energy availability since the 1960s.  

In 1910, Procter and Gamble patented the process of hydrogenation, which creates liquid vegetable oils from industrial seed crops. The additional energy from seed oils initially displaced carbohydrates, which trended down until the 1960s. 

Towards the end of the Vietnam War, food became scarce, prices soared due to inflation, and the population was getting hungry.  So, with an election imminent, President Nixon appointed Earl Butz as Secretary of Agriculture with a mandate to reduce the cost of food.  

The US Department of Agriculture forced farmers to use aggressive farming techniques, such as planting their entire fields ‘from hedgerow to hedgerow’ (rather than using crop rotation to let the soil rest and regenerate) and liberally using synthetic fertilisers. Farmers had to ‘get big or get out’. 

This led to an increased abundance of energy from both fat and carbs, which enabled the burgeoning processed food industry to create foods with the perfect combination of protein, carbs and fat to hit our bliss points. 

Targeting Our Bliss Points

In the 1980s, food companies learned to design their products to hit our macronutrient bliss points with engineering precision.  That is, create the perfect blend of nutrients to maximise consumption. 

Researcher and psychophysicist Howard Moskowitz spearheaded the 1970s optimisation of food to hit our bliss points and laid the foundation for the ultra-processed food industry. 

Notice how closely the bliss points shown in the chart below (created from more than a million days of data) align with the macros in our modern food system in the chart above.  Around 38% fat, 48% carbs, and 12% protein is the basic formula for all the ‘addictive’ foods we can’t stop eating. 

Prioritising protein-rich foods and meals enables us to avoid this magical autumnal bliss point formula. 

The Celebrations that Derail Our Best Intentions

Despite modern food technology, we still see some circannual trends in our nutritional intake.   This first chart shows the average weekly energy intake across the year collected over the past six years from 155,676 days of food logging from 16,661 Optimisers

At first glance, the main factor appears to be our annual celebrations: 

  • We start the year with the best intentions, and then along comes Easter with unlimited chocolate that we can’t resist! 
  • As the end of the year approaches, Americans have an onslaught of Halloween, followed by Thanksgiving and Christmas, again with unlimited tasty food and food-focused celebrations. 

It’s almost as if the deck is stacked against us to ensure we never reach our goal weight!

Note:  Our Optimisers live all over the world, but they’re predominantly from the northern hemisphere, particularly the USA.  We would likely see more substantial seasonal variations if we looked at data only from one hemisphere, particularly further from the equator, where the seasonal swings in climate are more significant.   

Celebrating Seasonal Harvests

Our modern holidays and celebrations undoubtedly have a massive impact on what and how much we eat throughout the year, which in turn affects our waistlines. The chart below shows how our weight oscillates around holiday celebrations. 

But what if there’s more to it than just the holidays on our modern calendars and Cadbury’s marketing engine at play to make us eat more chocolate at Easter? 

What if there’s something baked into the natural seasonal variation in our food system?

To find out, let’s dig a bit deeper into the history of our modern holiday celebrations. 

Easter

While we often think of Easter as a Christian holiday, it also has roots in pre-Christian pagan traditions. 

Easter is derived from Eostre, the Germanic goddess of spring and fertility.  Eggs and rabbits are symbols of fertility and rebirth after winter. 

Many ancient cultures celebrated the arrival of spring with festivals that included feasting, dancing, and rituals to welcome the renewal of life.

Thanksgiving

Similarly, Thanksgiving originated in celebrating the end of the summer harvest.  Many ancient civilisations, including the Egyptians, Greeks, and Romans, also held feasts to celebrate the harvest and thank their gods for the bounty

Native American tribes have a long tradition of celebrating the harvest with feasts and communal gatherings.

Halloween

Halloween’s origins date back to the Celtic festival of Samhain, which marked the end of the harvest seasons and the beginning of winter, a time associated with death (which our modern food system has saved us from).   

Christmas

Before Christmas, the Romans celebrated Saturnalia, honouring Saturn, the god of agriculture, between 17 and 23 December.  Yule, celebrated by the Germanic people, coincides with the winter solstice. 

In summary, we’ve always celebrated our harvests with food-focused celebrations. 

To create the charts below, I ran a 13-week rolling average (i.e. one quarter of the year or a season) to understand how different nutrients vary across the year. 

Energy

The first chart shows the variation in energy.  Unsurprisingly, we eat the most in autumn around the major end-of-year celebrations (i.e. Halloween, Thanksgiving and Christmas), with an extra 40 calories per day above average.   Meanwhile, we see the lowest intake, with about 35 calories per day less in winter. 

What surprised me was the peak in spring.  I expected spring to be a protein-sparing modified fast with high protein and lots of fibre.  However, spring also coincides with historical harvest festivals.  

Annual Protein Variation

Next, let’s examine macronutrient variation.  Protein is primary, so it’s the best place to start. 

We eat more protein (in grams) in spring (other than the dip sight dip at Easter when we mostly eat chocolate) and in autumn around the festive seasons.  Our protein intake has a close positive association with energy intake (R2 = 87%).  That is, when we eat more protein, we eat more overall. 

Our analysis of nearly a million days of data also shows that a higher absolute protein intake (in grams) corresponds with eating more. 

But it’s also worth noting that our protein intake has the smallest peak-to-trough variation of any nutrient (2.7%). Optimisers eat only 3 grams more protein in autumn than in winter. 

Unlike fat and carbs, which vary with the seasons, protein intake is locked in throughout the year. This suggests that we crave just enough protein but not too much. 

Protein is hard to overeat.  Regardless of the season and the foods available, our appetite ensures we get the protein we need.  But because there isn’t much storage space for extra protein, we quickly experience sensory-specific satiety and get tired of food that contains more protein than we need.  

But instead of focusing on eating more protein, a higher protein percentage aligns with greater satiety and eating less.  The percentage of protein in our food negatively correlates with energy intake (R2 = -84%).  That is, when protein % is lower, we eat more. 

In line with protein leverage, we eat more when the available food has a lower protein % (and vice versa).

The chart below shows that our Optimisers see the lowest protein % around Christmas and the highest protein % in summer.   

Again, the variation in protein % is small.  Optimisers consume 32.5% protein in summer and 31.5% in autumn.  To move from our natural fat gain to fat loss setting, we only need to make a modest shift in protein % (by reducing energy from fat and carbs while prioritising protein). 

Carbohydrate’s Summer Peak

While our absolute protein intake protein remains locked in, we see a significant swing in carbohydrate intake in both absolute and percentage terms (9.6% and 8.5%, respectively) and a much looser correlation with energy intake (R2 = 27% and -22%, respectively). 

Note the distinct peak in carbohydrate intake in early summer (when energy intake is low), with a much lower carb intake in winter. 

Fat Keeps Us Warm in Winter

But the reality is, our body doesn’t mind much if we get more energy from fat or carbs, so long as we get enough energy. 

Fascinatingly, the peaks and troughs in fat intake align closely with the maximum and minimum energy intake (R2 = 85%). 

With carbs high in summer, fat bottoms out.  Meanwhile, carbs are much lower in winter, and fat rises to fill the energy deficit.   

The Fat and Carb Combo

When we look at the three macros together, the first thing that jumps out is that our protein intake is remarkably stable across the year. 

Meanwhile, energy from fat and carbs oscillates depending on food availability in the different seasons, even in our modern environment with so many processed foods designed to be shelf stable until the end of the world. 

When we remove protein and double-click on fat and carbs, the energy from fat and carbs oscillates independently.  But we eat more when they come together in similar amounts in late autumn. 

Fibre Peaks in Spring

Fibre isn’t something we focus a lot on in our programs — people who get plenty of minerals and vitamins they need also get plenty of fibre.  

But it’s interesting to note how fibre peaks at the end of spring when plenty of minimally processed non-starchy vegetables are available.  Meanwhile, fibre decreases towards the end of summer when grains start to dominate. 

Seasonal Caffeine Consumption

While not a macronutrient, we enjoy more caffeine in spring to stimulate us as we come out of hibernation and want to be awake longer.   There is a 12.5% difference between the winter minimum and spring maximum caffeine intake. 

Caffeine intake doesn’t correlate with overall energy intake (R2 = 1%).  So, if you enjoy caffeine, go for it, but it won’t necessarily make you lose or gain weight. 

Alcohol Intake Variations

Meanwhile, we seem to enjoy alcohol more to celebrate Easter and even more in winter to warm us up around the end-of-year celebrations.  

There is a relatively significant (27%) difference in absolute alcohol intake between the spring trough and the winter indulgence. 

The strong correlation between alcohol and energy intake (R2 = 51%) makes sense, given we are more disinhibited and less mindful of our food intake when alcohol is involved.  

Alcohol provides energy that, due to oxidative priority, we need to burn before we use the energy in our food or the fat stored on our bodies. 

Top Nutrients Our Body Craves

To summarise the insights from this data, the table below summarises the variation in nutrients, from peak to trough, across the year. 

  • Even more than energy, we tightly regulate our protein intake (both in grams and percentage terms) because protein is the most critical macronutrient for survival. 
  • At the other end of the spectrum, alcohol is a nice to have that varies around celebrations.  But it’s not an essential nutrient like protein. 
nutrientvariation
protein (g)2.7%
protein (%)2.7%
fat (%)4.4%
energy (cal)4.9%
fat (g)8.2%
carb (%)8.5%
carbs (g)9.6%
alcohol (%)18.4%
alcohol (g)27.4%

The Key to Satiety

The table below summarises the correlation of each nutrient with energy intake. 

  • Increasing your protein % (by dialling back fat and/or carbs) has the most significant impact on eating less. 
  • For our lower-carb Optimisers, swapping out some fat for some carbs aligns with eating a little less (R2 = -22%), while simply eating more carbs aligns with eating more (R2 = +22%).  
  • Increasing your fat or alcohol (in absolute or percentage amounts) aligns with eating more. 
  • Eating MORE protein aligns with eating more total energy.  Hence, if our goal is greater satiety and cruising our cravings, our focus must be dialling back energy from fat and carbs while prioritising protein (not just eating more protein). 
nutrientR2
protein (%)-84%
carb (%)-22%
carbs (g)27%
alcohol (%)31%
fat (%)50%
alcohol (g)51%
fat (g)85%
protein (g)87%

For more inspiration for protein-rich foods with a higher protein %, check out our protein-rich foods here

Circannual Nutrition in Our Modern World

So what does all this mean for you and me today, living in our modern food environment where we are less exposed to swings in nutrient availability due to the seasons? 

Wintertarians vs. Summertarians

Viewing our food choices through a circadian nutrition lens gives us an interesting perspective on extreme diets and the passionate communities that gather around them.  The other side is the sworn enemy that all in the cult shall deride.

  • We could reframe keto, carnivore, low carb, etc., as Wintertarians or the people who believe that reducing carbs is the only way. 
  • Meanwhile, the people who passionately follow a low-fat or plant-only diet could be the Summertarians

But the reality is that both have just found a way to escape the trap of perpetual autumn, preparing for a winter that never comes. 

Circannual Nutrition and the Randle Cycle

The Randle cycle is a concept in biology that describes the competition between glucose and fatty acids for oxidation in muscle and other tissues.  

When fatty acids are abundant, glucose oxidation is inhibited (and vice versa).  This metabolic pathway ensures that the body efficiently uses available nutrients and conserves others.

But it becomes less efficient when we simultaneously get an oversupply of glucose and fat.  Professor Bart Kay uses the analogy of multiple people trying to use a revolving door simultaneously.  Not only do we eat more when our food contains a blend of fat and carbs, but we also use that fuel less efficiently. 

This is an essential feature if you’re a bear preparing for winter hibernation (the two photos below are both of Beadnose the bear, just a few months apart), but not so great if you want to lose some weight and escape our infinite autumn.

Our data analysis suggests that people eat less on a very high-carbohydrate OR lower-carb diet.   The key is moving away from the carb bliss point.  Our data suggests that reducing your carbs from 48 to 20% will give you a significant satiety benefit.  However, cutting carbs further isn’t necessarily better and can lead to more energy-dense and less nutritious food choices.   

The Importance of Nutrient Density

While protein is the dominant satiety factor, all the minerals and vitamins play a role in satisfying our cravings.  

Our biology naturally draws us to eat more of the foods that give us just enough nutrients with the maximum amount of energy to help us prepare for winter. 

To maximise profit, our modern food system has done a great job designing food products to hit our bliss points, which tells our bodies that winter is coming and we need to eat more and store fat to survive.  

Foods to Avoid

The simplest way to apply this knowledge is to avoid food products that list combinations of refined seed oils, sugar, flour, synthetic fortification, flavours and colours. 

You can be assured that any products in the centre aisles of your supermarket that follow this formula have been designed to hit your bliss points to maximise profit at the expense of your health.

When you start examining nutrition labels, you’ll be surprised at how many food products follow this formula.

Proactive Nutrition Tips

Parties and celebrations like Christmas and Easter will always come our way.  So it’s wise to be proactive most of the time and focus on fresh, nutrient-dense foods that boost satiety by providing more nutrients we crave without excess energy. 

For more inspiration, check out our infographics and printable lists of nutrient-dense foods here

To see what a week of maximum nutrient-dense eating looks like, download our Maximum Nutrient Density Meal Plan here.

Once your body is replete with all the nutrients it craves, you will be immune to the seduction of the constant barrage of foods designed to fatten you for a winter that never comes. 

Seasonal Eating Summary

Understanding circannual nutrition offers a fascinating glimpse into how our bodies are naturally tuned to seasonal food availability.  

The availability of energy from fat and carbs naturally varies throughout the year.  But modern ultra-processed foods leave us stuck in autumn, preparing for winter. 

With a deeper understanding of your biology and seasonal eating patterns, you can reverse-engineer your nutrition to eat healthier and manage your weight year-round.  

To avoid autumnal foods that stimulate our appetite, focus on protein-rich, nutrient-dense, seasonal foods.

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2 thoughts on “Circannual Nutrition:  The Natural Seasonal Cycle of Carbs & Fat Revealed”

  1. Brilliant analysis of the seasonal variations of eating habits. I have long recognised it was easier to lose fat in summer and come autumn/winter, I just felt I had to eat! I know the moment the day length shortens in October I start to crave more food – so interesting. Thank you for this fascinating article.

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