CHAPTER 6 – Reappraising Dr Leaf

In the first two sections, I outlined the current scientific concepts of thought and stress, and the basic science behind them.  In this short chapter, I want to bring everything together.

I will compare the fundamentals of Dr Leaf’s teaching with the current scientific research and models I’ve outlined in the beginning of the book.  I will use illustrative quotes from her books to show that I’m not misrepresenting her.  Then I’ll discuss what the scientific literature suggests, allowing you to compare them.

In my introduction, I proposed that the fundamental arguments of Dr Leaf’s work are

1. Thought is the main driving force that controls every other aspect of our lives (and our physical world).
2. We have full control over our thoughts.
3. Thought causes stress.
4. Stress is directly responsible for nearly all serious physical and mental illness.
5. Since thoughts cause stress, and stress is directly responsible for the vast majority of human disease and suffering, thought therefore causes the vast majority of human disease, making thoughts toxic.  If toxic thoughts cause disease, “detoxing” thoughts will cure or prevent disease.

Let’s review these, one by one.

1. Thought is the main driving force that controls our lives (and our physical world).

Dr Leaf’s teaching:

“Thoughts influence every decision, word, action and physical reaction we make.” [1: p13]

“Our mind is designed to control the body, of which the brain is a part, not the other way around.  Matter does not control us; we control matter through our thinking and choosing.” [2: p33]

“Research shows that 75 to 98 percent of mental, physical, and behavioural illness comes from ones thought life.” [2: p33]

“DNA actually changes shape according to our thoughts.” [2: p35]

“The main point in this chapter is that mind controls matter.” [2: p38]

“It is very interesting that every cell in the body is connected to the heart, and the brain controls the heart, and the mind controls the brain.  So whatever you are thinking about affects every cell in our body.” [2: p94]

“Everything you do and say is first a thought in your physical brain.  You think, then you do, which cycles back to the original thought, changing it and the thoughts connected to it in a dynamic interrelationship.  If your thinking is off … then your communication through what you say and do is off, and vice versa.” [2: p98-9]

“Quantum theory converts science’s conception of humans from being mere cogs in a gigantic, mechanical machine to being freethinking agents whose conscious, free choices affect the physical world.” [2: p120-1]

“Thought signals seem to move faster than the speed of light and in ways that classical physics cannot explain.  This means our mind controls matter, and is therefore a creative force.” [2: p121]

The scientific response:

Thoughts do not control our brain, our lives, or physical matter.  Thoughts are a function of our physical brain, one small part of our brains overall activity.  Thoughts are not faster than light, and they do not control physical matter.

Specifically, thoughts are an explicit (conscious) projection of information, formed as working memory utilizes a larger area of cerebral cortex to process specific parts of a much larger, ongoing stream of information, as directed by the implicit executive systems of our brain.  Thoughts are like the image on the monitor on your computer.  Billions of calculations are being performed by your computer every second, but all you see of them are what is projected onto your monitor.

Thoughts, and the mind, are a product of the brain.  They do not control the brain.  Disorders of the brain, such as tumours or infections, confirm the influence of the brain on our thought content.  Again using the computer/monitor analogy, the information on the monitor doesn’t control the billions of calculations going on underneath, the billions of calculations controls what is on the monitor.

Dr Leaf uses the term “thought” to refer to all brain activity, but her definition is so broad that she invalidates her own arguments.  The structure of the brain changes during thought, but the structure of the brain changes with all activity of the brain, just like the structure of all tissues changes with its use. Thought is not required for neurological changes to occur. 

If thoughts cannot control the brain, then they certainly cannot control any other form of matter.  This is intuitively obvious, because you can’t think yourself thinner, think yourself taller, or think yourself younger.  You can’t move objects with your mind, change the weather, or change other people.  Thought does not control matter.

2. We have full control over our thoughts

Dr Leaf’s teaching:

“We have two choices, we can let our thoughts become toxic and poisonous or we can detox our negative thoughts which will improve our emotional wholeness and even recover our physical health.” [1: p21]

“Free will and choice are real, spiritual and scientific facts.” [2: p25]

“Your body is not in control of your mind – your mind is in control of your body.” [2: p25]

“We are not driven by forces beyond our conscious control.” [2: p42]

The scientific response:

Thought is the conscious awareness of a much greater stream of information processing.  It is the brain’s working memory engaging a larger area of the cerebral cortex to process more important information.  It can appear that we have control of our thought process, because it seems that we can direct our attention to a task or problem.  Yet, if we were to have full control over our thoughts, then we could never experience daydreaming, or those “eureka” moments of inspiration, which occur without the control of our attention.

In neurobiological terms, control over our thoughts comes with engaging the central executive network.  But the default mode network is not associated with complete control over our stream of thoughts, and since the default mode network is, quite literally, the default mode, it is clearly incorrect to suggest that we have complete control over our thought process.

Similarly, although our actions and our thoughts seem as though they are under our full control, many scientists have shown that free will is an illusion, with experiments showing repeatable and predictable brain activity up to 8 seconds before a person was aware of the choice they would make.  And as shown by models like the Cognitive Action Pathways model, there are many variables that feed into our thoughts, such as genetic changes to our perception, our personality, and our physiology.  At best, we have partial free will, limited by our genetics and the underlying information processing of our brain.  

3. Thought causes stress

Dr Leaf’s teaching:

“The result of toxic thinking translates into stress in your body.” [1: p15]

“Stress is a global term for the extreme strain on your body’s systems as a result of toxic thinking.” [1: p15]

“Stress is a direct result of toxic thinking.” [1: p29]

“These stages of stress are scientifically significant because they illustrate how a single toxic thought causes extreme reactions in so many of our systems.” [1: p39]

“As you think those negative thoughts about the future … that toxic thinking will change your brain wiring in a negative direction and throw your mind and body into stress.” [2: p35]

“This immediately puts the brain into protection mode, and the brain translates these poor-quality, toxic thoughts as negative stress.” [2: p36]

The scientific response:

Stress, as defined by Dr Leaf, is based on Selye’s General Adaptation Syndrome model.  Selye developed the General Adaptation Syndrome model based on the response of animals to physiological stressors.  He did not subject the animals to psychological stress.  So stress is not the direct result of toxic thinking, and ironically, the model of stress that Dr Leaf relies on contradicts her own teaching.  Other psychological models such as Dual Systems Model confirm that physiological stress is not thought dependent.

Psychological stress is not usually the result of the thought process either.  Conditioned fear occurs when a person or animal learns to associate a stimulus (a place, a smell, a sound, etc) with pain or distress.  According to the Dual Systems model, when the same situation is reencountered, the stimulus is processed by deeper brain structures (usually the thalamus), which subconsciously recognises the stimulus, and directly primes the stress system in readiness to respond.  Eventually the cerebral cortex catches up, and thinking takes place, reappraising the risk and refining the plan of action.  So stress is independent of our stream of thought. 

Rather, according to the Cognitive Action Pathways model, the stimuli are perceived, processed through the lens of personality and physiology and then processed by the executive areas of our brain that, if required, broadcast these thoughts into our consciousness.  Therefore, stress generates stressful thoughts, not the other way around.

Thoughts are often associated with stress, since the underlying common neurological and physiological processes often coincide, and our memory is designed to link the two.  But correlation is not the same as causation.

4. Stress is directly responsible for nearly all serious physical and mental illness.

Dr Leaf’s teaching:

“Hostility and rage are at the top of the list of toxic emotions; they can produce real physiological reactions in the body and cause serious mental and physical illness.” [1: p30]

“Let’s look closely at three systems that are particularly affected by stages two and three of stress: the heart, the immune system, and the digestive system. [1: p39-43]

“Even a little bit of these negative levels of stress from a little bit of toxic thinking has far-reaching consequences for mental and physical health.” [2: p36]

“The association between stress and disease is a colossal 85 percent.” [2: p37]

The scientific response:

Stress is associated with a small number of illnesses, but stress is not associated with the majority of human illness, and even if it were, correlation is not the same as causation.  Studies at the coalface of medicine in Australia suggest that presentations for non-physical illnesses (mental health, stress) only amounted to about eight percent of the total number of presentations.

While the majority of the population will at some point suffer an extended period of extreme stress, only a minority will go on to develop a stress related disease.

This is because most people have an inbuilt system of coping, which provides resilience against the effects of stress.  Animal models and some human cohort studies have shown that small amounts of stress actually improve function and health.

5. If thoughts cause stress, and stress is directly responsible for nearly all serious physical and mental illness, then thought causes the vast majority of human disease, therefore thoughts can be toxic.  If toxic thoughts cause disease, “detoxing” thoughts will cure or prevent disease.

Dr Leaf’s teaching:

“A massive body of research collectively shows that up to 80% of physical, emotional and mental health issues today could be a direct result of our thought lives.” [1: p15]

“Research shows that 75 to 98 percent of mental, physical and behavioural illness comes from one’s thought life.” [2: p33]

“We have two choices, we can let our thoughts become toxic and poisonous or we can detox our negative thoughts which will improve our emotional wholeness and even recover our physical health.” [1: p21]

“Making your thoughts life-giving, not life-threatening, means you will be far less likely to suffer sickness and disease.” [1: p43]

The scientific response:

“Toxic” thought is not the major cause of human disease.  Therefore, “detoxing” from negative thoughts does not significantly improve human health.

The major cause of illness across the world is infectious diarrhoeal disease, which is related to clean water and sewerage systems.

In the western world, infectious diseases are limited by our easy access to fresh water and internal plumbing.  The techniques and technology of modern medicine, such as public health campaigns for pap smears, modern midwifery, and vaccinations, also prevent many deaths.  Cervical cancer, complications of childbirth, and infectious diseases like measles, are not thought related.

Because of the success of modern medicine in treating and preventing these illnesses, chronic diseases, mental health disorders and “stress-related” illnesses have become more prominent, giving the false impression that thought and stress significantly contribute to human health and disease.

Considering health in the overall global context, and by taking into account the effects of medical science on our society, it can be easily seen that thought life could not cause anywhere near 75 percent, let alone 98 percent, of physical and psychological illnesses.  The figure proposed by Dr Leaf is therefore grossly exaggerated.

Analysis of the “massive body of research” which Dr Leaf used to arrive at her figure shows that it is based on cherry-picked, out dated and/or non-peer reviewed references. 

A full analysis of Dr Leaf’s sources, and the current scientific literature that contradicts her, is documented in Chapter 10.


So, if thought is not the driving force of our cognition, and thought is not under our full conscious control, and if thought does not cause stress, and stress does not cause most of the maladies of human kind, then it would be fair to say that even if it were possible to change your thoughts, changing your thoughts would not restore your emotional and physical health.

Dr Leaf’s teaching does not align with current scientific knowledge.