When it comes to food and health, it's not all about how much we eat. It's not all about what we eat. It isn't all about the exercise/physical activity we do, or even how well we've been sleeping. As much as these things influence our appetite, food choices, and how our bodies process what we eat, there is at least one more factor that I think is underrated and under-researched – how we feel when we eat. That we make poorer food choices when we eat in response to our emotions or when we're very hungry probably isn't very controversial. You can test it on yourself by observing what you eat, or feel like eating, the next time your upset or ravenous.
Food choices aside, the mental/emotional state you're in when you eat matters irrespective of your food choices. Have you ever been so stressed or upset that you were put right off eating? Or have such unhappy bowels that you find it hard to concentrate on anything else? Those are sobering illustrations of how much your mental state and your digestive system influence each other. This strong relationship between our brains and our digestive system is well documented (1-3).
Extremes aside, does the state you're in when you eat matter? The answer is a resounding yes. It's not my idea, it's not a new idea, but it isn't exactly given much air time. The question is why, and for a scientist like me — how? The physiology of stress and relaxation continue to be a hot topic of research, as does the process of digestion, but the two are seldom looked at together. This should be perplexing given that the extremes of the states we can be in are often referred to as rest and digest, and fight or flight.
Where we are along the spectrum of fight/flight vs. rest and digest is controlled by part of our nervous system known as the autonomic nervous system; think automatic, because it controls things that need to happen even when we aren't concentrating on them, e.g. our breathing, heart rate, blood pressure, and digestion. The two sides of the autonomic nervous system, the sympathetic and parasympathetic systems, are in a constant tug of war pulling us between fight/flight, and rest and digest. Or put another way, between stress and a relaxation.
When our survival depends on fighting or fleeing, our sympathetic nervous system pulls hard to ensure our fuel stores, i.e. glucose (‘sugar’) and fat, are released from storage into the blood stream, and that this energy rich blood goes primarily to the muscles that need it 4. One key way it does this is by causing the release of the stress hormones cortisol, adrenaline and noradrenaline (epinephrine and norepinephrine for US readers). These hormones signal the liver to make and release glucose, and the fat cells (adipose tissue) to release fat. Cortisol also directly interferes with the actions of the hormone insulin, which is responsible for controlling glucose and fat levels in the blood, and assisting protein in getting into cells, especially muscle.
The problem is that many of us experience chronic stress. Stress from things we're unlikely to either be able to fight or flee effectively. Stress not from physical danger, but traffic jams, financial worries, and relationship problems. As a result of this unresolved foundation of stress, our sympathetic nervous system dominates our bodies too much of the time. Being trapped in various degrees of fight/flight interferes with our digestion and metabolism of food.
Having cortisol and other stress hormones making sure our blood is already full of glucose and fat when we eat is not a good idea. It forces our bodies to deal with the fat and carbohydrates, and hence glucose, in the food we eat as well as that released from our stores. And insulin, the hormone in charge of the cleanup is at a disadvantage because it has to contend with cortisol. In addition, blood is directed to the muscles, not the bowels, when we are stressed. That almost certainly doesn’t help digestion.
On the other, when we are relaxed and eat, our blood is directed to our bowel where it ensures our internal organs can do their work efficiently and make sure we get the greatest benefit from our food. When relaxed our blood glucose and fat are likely to be appropriately low in anticipation of the fresh supply from food. And, once nutrients from our food start entering our blood, insulin can do its job without contending with the opposing effects of stress hormones like cortisol.
How do we achieve relaxation needed for good digestion and healthy metabolism? There are plenty of options to get some relaxation into our lives, but in the context of eating the most obvious are:
- Take time to prepare and really focus on food preparation while you do it;
- Whether or not you prepared the food, take 5 slow deep breaths before eating; and
- Focus on the act of eating by minimising distractions, eating slowly, chewing thoroughly, and paying attention to taste, flavour, and texture.
That also means no TV, internet, reading, driving or other distracting activity while eating no matter how much of a multitasker you pride yourself on being. A pleasant conversation with others sharing the table being the exception.
The very act of eating can help put you into the more relaxed rest and digest state if you give it half a chance. So, enjoy your food by taking time to savour the flavour. The added benefit is that you’ll end up making better food choices when you actually pay full attention to what you are eating.
A version of this article first appeared on www.profgrant.com.
1. Bailey, M. T. Influence of stressor-induced nervous system activation on the intestinal microbiota and the importance for immunomodulation. Adv. Exp. Med. Biol. 817, 255–276 (2014).
2. Gareau, M. G. Microbiota-gut-brain axis and cognitive function. Adv. Exp. Med. Biol. 817, 357–371 (2014).
3. Omran, Al, Y. & Aziz, Q. The brain-gut axis in health and disease. Adv. Exp. Med. Biol. 817, 135–153 (2014).
4. Frayn, K. N. Metabolic Regulation. (Blackwell Pub, 2010).
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