If you haven’t read the first part of this series (click link), it is well worth your time, as I will build on information about hormones and the way we control food intake, which I introduced in that article.
- We have three levels of “control”, which determine our actions.
- Pavlovian control is subconscious and favours pleasure and reward. It likes cake.
- Habitual control is based on previous experiences, making you repeat actions you enjoyed previously. Like eating cake.
- Goal-directed control is the most conscious level of control, and you use it to predict future outcomes of actions, such as eating less cake to prevent weight gain.
- The body uses many hormones, including insulin and leptin (make you feel full) and ghrelin (makes you hungrier) to help guide when and how we eat via opioids and dopamine in the brain.
- We only have the capacity to make a limited number of decisions. If you spend all day thinking at work, you are much more likely to let habitual and pavlovian control take-over, which leads to less sensible food choices.
- Planning meals in advance will remove the need to make food decisions when hungry.
Why do we overeat?
As I started writing part 2, I was reminded of this article, which I read a few months ago. It was written by a doctor in the UK, who provides a call-to-arms for doctors to stop avoiding uncomfortable conversations with patients and face the obesity epidemic head-on.
I completely agree that frank conversations with patients, as well as significant lifestyle changes, are essential in our global battle to fight obesity and the associated complications. I have also experienced first-hand the frustration associated with both patients and doctors skirting around the issue. While the article is well-informed regarding the devastating effect that obesity is having on the NHS and healthcare systems worldwide, I disagree with the author’s suggestion that obesity is just a “mindset” that patients are unwilling to change.
Despite what the author suggests, the advice to “eat less” has never been a robust weight-loss strategy. This article will cover some of the reasons why:
- Our natural pleasure and reward mechanisms drive us to eat convenient, hyper-palatable foods that are high in sugar and fat and often low in nutritional value.
- When we are stressed and sleep-deprived, we lose control of our ability to make sensible food choices. The drive to eat sweet/fatty food increases.
- The modern foods, and particularly the added fructose, we eat bypass the mechanisms that the body uses to feel full.
- Once we’re obese or diabetic, we lose our hormonal control over food-intake, and are essentially always “hungry”.
Through the majority of our time as a species, our daily stressors involved a scarcity of food and threat to life, either from predators or disease. In these stressful situations, the body releases a “stress” hormone – cortisol. Cortisol acts on the brain to reduce our “goal-directed” executive control and increase our emotional drive to eat foods high in sugar and fat. When you’re being chased by tigers, this makes a lot of sense – you want to think less, and eat food that will fuel you for as long as possible. The rewarding effect of eating high-sugar foods also acts directly in the brain to improve mood when stressed.
We know that modern pressures, from work and home life, have exactly the same effect on our eating habits. In the face of chronic stress, we lean towards comfort foods, which have a sweet flavour and fatty texture. Though one episode of comfort eating will never make us fatter, repeating this behaviour has a profound effect on future food choices.
As cortisol tends to override our executive control, we know that continued stress will force us to rely on our “habitual-control”. Once the association is made between comfort foods and feeling better, a subconscious habit is formed. This then induces comfort eating at lower levels of stress, as it becomes easier to subconsciously mimic previous actions.
Chronic stress can then increase the risk of weight gain and obesity:
- At least 40% of us gain weight when stressed.
- The effect is greater in women than men, but your risk of weight gain due to stress is also greater in those who already weigh more. This is thought to be at least partially due to the fact that insulin levels increase as weight increases.
You might remember from part 1 that, when insulin control is normal, increases in insulin after a meal act alongside leptin to increase satiety and reduce the drive to eat. However, when cortisol is also raised, it acts together with insulin to increase fat storage.
Nowadays, the easy access to cake when we are stressed due to juggling jobs and kids means our natural hormonal responses act on both our brain and body to make us gain weight.
Sleep deprivation is one of the most common modern stressors, but also has a very specific detrimental effect on our hormones, our ability to think clearly, and the food choices we make. Sleeping for four hours a night for just a few days will:
- Increase cortisol.
- Impair control of insulin and glucose levels.
Sleeping less than 7-8 hours per night is a risk factor for obesity, and the trends towards decreasing sleep and increasing obesity have occurred simultaneously in recent years. In rat models of sleep deprivation, we know that restricting sleep:
- Increases ghrelin (makes you hungrier)
- Reduces leptin (makes you hungrier).
- Causes overeating and weight gain.
Though rat studies never fully explain what goes on in humans, we see consistently elevated ghrelin after sleep deprivation in humans. More importantly, those who are sleep deprived are correspondingly hungrier throughout the next day.
Recently, some very tightly controlled studies have shown that sleeping for 4-5 hours (compared to 8 hours) increases calorie consumption by more than 10%.
Though there is often an increase in the total energy we burn when we sleep less, we always over-compensate in our calorie consumption. In fact, further studies have shown that the areas of the brain associated with reward from food are more greatly activated when you are sleep deprived. This increases food intake throughout the day, particularly from snacks.
Cutting your sleep short for even just a few days at a time will make you hungrier, increase your pavlovian drive to eat sugary and fatty foods to satisfy your reward centres (due to increased ghrelin), and cause you to over-eat.
Get more sleep.
The subject of sugar in the diet is currently quite topical. Last week, a group of doctors in the UK began campaigning to reduce the sugar in food by 20-30% as part of their “Action on Sugar”, and rightly so. Our obesity rates are closely correlated with increased sugar intake. Increasing sugar has also been linked to an increased risk of type 2 diabetes, even in those who don’t become overweight.
This boils down to two things:
- Sugar has a potent effect on the reward-based centres of the brain.
- Modern sugars can even trick us into eating more.
Firstly, unlike fat and protein, the more sugar we eat, the greater the reward and, ultimately the more calories we tend to consume. Anything sweet in the diet will activate our reward centres, which results in:
- Reinforced sugar cravings driven by pavlovian (subconscious) control.
- Formed habits that are more likely to make you eat sugar in the future.
Even eating things that have artificial sweeteners in (such as “diet” drinks) will later result in increased sugar “cravings”. This only means one thing - cake.
While every cell in the body uses glucose for energy, most cells lack the ability to use fructose. As a result, almost all of the fructose we eat is handled by the liver. The liver is very good at using fructose (and glucose) to create glycogen as a store of energy. However, when the liver has reached full glycogen capacity, it begins to turn all the extra fructose into fat to be stored around your midsection.
When we eat (or drink) a meal heavy in fructose, the following things happen:
- Intense activation of the pleasurable reward-based centres of the brain.
- No increase in insulin (still hungry).
- No reduction in ghrelin (still hungry).
Therefore, fructose rewards our need for sweet food, but doesn’t activate the normal signals that the body uses to let us know that we’ve eaten and are full. This leads to more eating, stronger habitual drive to eat sweet foods and, inevitably, weight gain.
Now, if we look at modern foods, “high fructose corn syrup” (also known as HFCS or glucose-fructose syrup) is added to almost every soft-drink and processed food because it is very cheap and very sweet. A number of “healthy” sweeteners (such as agave syrup) and most fruit juices are also pure, unadulterated fructose. When fructose is packaged in an apple, the negative effects are largely diminished. However, once taken out from the crunchy, fibrous delivery system, things are very different.
Finally, though fructose is often lauded for diabetics because it doesn’t raise blood-sugar levels like table sugar or glucose might, this is not a good thing. Excess calories from fructose (like chugging a large soft-drink at the cinema) increase the fat in our blood and worsen insulin resistance. These are two cores features of obesity and type 2 diabetes.
You can’t just “eat less”
Things then become even worse once our stressful, sleep-deprived lives have resulted in weight gain. Though we’re still building up a picture of how our hormones change in diabetes and obesity, we tend to see these trends:
Obesity: Abnormally high levels of insulin, leptin and ghrelin.
Diabetes: Abnormally high levels of insulin and leptin, with low ghrelin.
As low ghrelin usually means less drive to eat, you might think that diabetics tend to be less hungry. However, diabetics actually have worse satiety after a meal, despite the levels of ghrelin. This is signifies of a loss of control of hunger.
From the summary of hormonal changes above, you’ll also see that both insulin and leptin tend to increase as we lose control of our blood sugar (diabetes) and become fatter (obesity). As we covered last time, leptin acts in the reward centres of the brain to reduce dopamine signalling, make food less rewarding and eventually stop us eating any more. However, as leptin and insulin increase in obesity, two things happen:
- Dopamine signalling gets forced lower and lower.
- Insulin and leptin resistance begin, and the body no longer uses them as signals to stop eating.
The effect of reduced dopamine signalling instead causes a continued “craving” for reward. In obesity, high leptin levels produce a state of artificially low “pleasure”. As a result, the body tries to compensate by eating more “rewarding” foods, similar to what happens in drug addiction.
In obesity and diabetes, not only has the body lost the normal signals we use to tell us we’re full, the altered hormone levels inhibit the reward centres of the brain in a way that creates a constant drive to find pleasure from food.
Here is the simple upshot:
In obesity, it is harder to make “healthier” food choices and almost impossible to adequately satisfy food cravings even when you have eaten enough.
Most obese people know that they should eat better and lose weight to improve health. It’s not that they don’t care, they just face an increasingly difficult battle against subconscious behaviour. Though it may sound glib, imagine trying to tell a drug addict that they HAVE to have some drug in order to survive (we all need food), but that they are only allowed a little bit of it.
IT’S NEVER GOING TO WORK!
All this begs the question – if our lifestyle and subconscious drive have a huge sway on what we eat – how on earth can we lose weight, improve health and stay that way for a long time?
Looking over the information above (and from last time), some rules about how and what we should eat become apparent:
- We shouldn’t feel as if we are continuously denying ourselves.
- It is very difficult to lose weight by eating less of what we’re already eating.
It is not going to be easy, and much of it has to come from willingness of an individual to work hard, rather than sweeping healthcare reform. As both doctors and patients, we need to realise that every detrimental aspect of lifestyle will need to be managed.
Here is how we can tackle some of the key areas:
Change what you eat: A huge part of breaking the cycle will involve reducing intake of refined carbohydrates and sugar, particularly from processed food and fruit juice. A number of trials have shown that adopting a Mediterranean diet low in sugar and high in healthy fats from olive oil, fish and nuts leads to greater fat loss and reduced risk of cardiovascular disease, diabetes and obesity compared to a low-fat diet.
Additionally, in trials of a “paleolithic” diet, participants naturally eat less due to the “satisfying” nature of the food. Initially based on what our ancestors evolved to eat, the modern approach to this diet focuses on:
- Foods that we know improve health (lots of fresh vegetables, salads and healthy fats and protein including oily fish and meat).
- Removing foods that may cause issues (such as grains, sugar and some dairy).
Importantly, you should focus on the fact that in one study, compared to participants on a Mediterranean diet, those on the paleolithic diet ate 25% fewer calories without being hungrier.
These participants saw a greater loss of waist circumference and improvement of leptin levels, most of which was attributed to swapping grains (wheat, flour, rice, oats etc) and sugar for more vegetables and fruit.
Though no dietary change will be perfect for everyone (and some people will need to make greater changes than others), swapping grains and sugar for healthy fats, protein and more fruits and vegetables will:
- Keep you full for longer and reduce snack cravings.
- Improve weight loss.
- Help re-gain normal hormone levels, which will return normal control of eating.
Improve activity: Exercise has a huge part to play in any attempt at fat loss and improved health. For diabetics, just one session of aerobic exercise is enough to reinstate normal feelings of fullness in response to glucose. Brisk walking for 30 minutes a day will reduce your risk of obesity, diabetes, heart disease and cancer. In addition, lifting heavy weights 2-3 times per week improves fat loss and insulin and blood sugar control. It will also keep you strong and sexy well into later life. I have covered the types of exercise that have been proven to improve health here.
Increase sleep: Good sleep is such a fundamental part of what makes humans healthy. Not only will increasing your sleep improve the hormonal imbalances caused by stress and diet, it will also reduce your risk of dementia and make sure you’re able to function maximally at both home and work. An extra hour or two per night could make all the difference. I’ve covered some basic tips on how to sleep better at the end of this article.
Reduce stress levels: As much as we may wish it were possible, we can’t all quit our jobs, pack the family off and just sit and relax all day on the beach. However, it goes without saying that removing unnecessary stress will automatically improve any attempt to improve weight and health. This could include anything that we tend to worry about constantly, including our weight. Studies have shown that women who worry about dieting and weight loss tend to eat more in response to the associated stress!
Thankfully, some research has also shown that practising mindfulness or meditation improves our ability to focus and use the prefrontal cortex for decision making. This can help keep goal-directed control in charge of what we eat and reduce the risk that we will succumb to cravings. The exact type of meditation is less important, but the effects on stress can be quite marked. For example, everybody has 8 minutes a day to meditate.
Take back control
If we try to battle through fat loss purely by torturing ourselves with fewer calories, a combination of pavlovian reward-driven eating and “decisional fatigue” (willpower failure) will make it almost impossible to lose weight and keep it off. However, once we begin to make the above changes, we can put ourselves back in control, and take huge steps forward in our fight both against obesity and for our individual health.
As with previous articles with a long list of references, you can find them all in the document below: