Why is seasonal eating better for our health, flavour and our pockets?
Seasonal eating might be the catch phrase of chefs worldwide, but before the day of the supermarket, we all ate seasonally, and often locally. Flavour is often the reason that chefs and foodies eat seasonally; but we’ve all eaten a dull, tasteless strawberry in February or a bland tomato in March. We are often advised to eat seasonally, not just for flavour but for the potential added health benefits.
With year-round availability of foods in supermarkets, we seem to have lost touch with nature and when local foods are in season. A BBC poll in 2014 of 2000 people showed that only 10% of people actually knew what fruit and vegetables were in season despite 86% saying how important seasonality and 78% who say that they shop seasonally. But how important is this to our health, and that of the environment?
Eating well is more than just flavour or solely about health. For me, this means eating a variety of different foods which maintain our health and well-being, giving us enough energy to do everything we want in our lives and stabilising our mood, and yet taste delicious. So, why does eating seasonally matter nutritionally and what other factors affect the nutrition of our food?
There are is also the question whether organic food has higher levels of nutrients than those grown with conventional farming, using pesticides. The nutrient quality of our food is affected by many factors, including how often the crops are harvested, when the crop is picked, the weather and the variety of the crop. As humans, we are omnivores and eat a range of animal products which can vary seasonally in nutrient density. Those that live in temperate and artic latitudes often have seasonal cycles of fattening and body weight.
A review of 26 studies and meta-analysis of looking at the effect of the seasons and how much we ate found that humans eat more in the winter and post-harvest. From winter to spring, we ate fewer fruits and more vegetables, eggs and alcohol. Going into summer, we ate more fruits and less cereals, and then into autumn, more fruits. Before the industrial revolution, our diet was coupled with seasonal cycles of food availability; does this mean that our metabolism developed along with our health requirements along the seasons?
As the seasons and weather change year to year, this affects the nutrient levels in our food, which also changes season to season. A micronutrient is a nutrient which is required by the body in small quantities for it to function well. Whilst there is a range of studies reviewing the micronutrient status of organically and conventionally produced foods, these studies have varying results.
A review published in 2011 of a near 30 year study found that the micronutrient levels of vegetables and legumes was higher in organic produce than in those conventionally farmed. Whilst much more research is needed to compare different agricultural practices and the impact on our health and well-being, this review did consider harvesting, crop varieties and soil conditions.
So is eating seasonally is better for you nutritionally? To answer this question, we need to consider research that looks as just one micronutrient in one food and is analysed at different seasons. A study in 2008 looked at both organic and conventionally grown broccoli in spring and in autumn in USA. Vitamin C was used as a biomarker in this study to test whether the nutrient status changed, as it is present in high quantities when harvested but degrades quickly compared to other nutrients. The broccoli harvested in autumn had higher levels of vitamin C for both those grown organically, and conventionally farmed. Vitamin C is sensitive to being stored so it’s better to eat sources of food that are both local and seasonal.
Food in season often comes as a glut at it’s seasonal peak – reducing the price whilst being full of flavour and nutrients. If we eat seasonally, we can reduce our food bills to take advantage of this glut and ensure that we are getting as much of nutrients possible from each food source. Freezing these foods maintains the majority of the nutrients so it’s a great way of making the most of seasonal foods, and preserving both nutrients and flavour.
So what’s in season in March:
Brussel sprouts, cauliflower, purple sprouting broccoli, cabbage, Pak choy
Brassica vegetables as high in sulphates and antioxidants which means that the reduce the risk of cancer. Cruciferous vegetables are very high in vitamin C, vitamin E, vitamin K, folate, selenium, glucosinolates, flavanoids, polyphenols, and other antioxidants and anti-inflammatory molecules. Diets high in these cruciferous vegetables reduce the number of sulphate reducing bacteria, which improves gut health.
Celeriac, sweet potato
Root vegetables such as these are packed with complex carbohydrates, antioxidants and fibre. The fibre contains polysaccharides which are anti-oxidants, anti-carcinogenic and anti-inflammatory. High fibre diets prevent inflammation and disease, and support digestion, and preventing IBS and constipation.
Jerusalem artichoke, Chicory, radicchio,
Jerusalem artichokes and to a lesser extent chicory and radicchio, are full of minerals and B vitamins, which are important for cardiovascular, nervous system, muscle and bone health. It is full of inulin, a powerful prebiotic which encourages the growth of beneficial bacteria and can help lower blood pressure.
Citrus fruits like grapefruit, lemon, oranges
The majority of the fibre in citrus fruits is mostly soluble fibre which helps to lower LDL cholesterol and regulate glucose levels. The remaining fibre is insoluble which adds bulk to our digestive system and reduces the risk of constipation.
Leeks, onion, spring onion
These roots contain high levels of antioxidant polyphenols and phytonutrients including allyl sulphide and quercetin. These alliums are powerful anti-inflammatory and prevent heart diease, cancer, lower LDL cholesterol and regulate glucose. They also are anti-bacterail and help protect against detrimental bacteria and the inulin supports the growth of beneficial bacteria.
Rhubarb contains high levels of anti-oxidants anthocyanin and lycopene, and potassium which reduces blood pressure. It is also a powerful laxative and full of fibre which will prevent constipation and relieve it.
On the value of seasonal mammals for identifying mechanisms underlying the control of food intake and body weight.
Seasonality of food groups and total energy intake: a systematic review and meta-analysis.
Evaluation of the micronutrient composition of plant foods produced by organic and conventional agricultural methods.
Nutritional quality of organic, conventional, and seasonally grown broccoli using vitamin C as a marker.