Science contradicts Dr Leaf
There are so many examples of Dr Leaf being directly contradicted by the science that she claims to have expertise that I don't have room to outline them all here. What I can do in this limited space is to outline Dr Leaf's most egregious and ironic fallacies as a taster. If you want more information, please download a copy of my free eBook
The 98 percent
One of Dr Leaf's most fundamental assertions is that “75 to 98 percent of mental and physical illness comes from ones thought life” . She uses this little factoid all the time to justify her belief in the power of thoughts.
However, her statement is completely wrong. When considered in the historical and global context , most of human illness is related to preventable diseases that are so rare in the modern western world because of generations of high quality public health and medical care.
For example, Hunter et al state that, “diarrhoeal disease is the second most common contributor to the disease burden in developing countries (as measured by disability-adjusted life years (DALYs)), and poor-quality drinking water is an important risk factor for diarrhoea.” 
De Cock et al write, “Recent estimates of the global incidence of disease suggest that communicable diseases account for approximately 19% of global deaths” and that “2.5 million deaths of children annually (are) from vaccine-preventable diseases.” 
Routine screening with the much-maligned pap smear has decreased the death rate from cervical cancer in women by as much as 83% . And having a competent midwife and obstetric support during childbirth can decrease the odds of dying in childbirth from 1 in 6 to less than 1 in 30,000 .
Midwives, vaccinations, pap smears, clean drinking water and internal plumbing have nothing to do with our individual thought life. We take all of this for granted in the first-world, so the impact of our thought life becomes artificially inflated. In reality, modern medicine and civil engineering, not our thought life, have everything to do with our good health..
Thought what makes this meme such a good example of the weakness of Dr Leaf's teaching is not just because it's contradicted by actual science, but in trying to justify her conjecture, Dr Leaf has resorted to twisting, misquoting, and generally fudging information from her 'sources' in order to make them support her false conclusions.
For example, Dr Leaf quoted a source on genetics that was over thirty years old, from a time when genetic studies were still in the dark ages. She also misquotes her sources, significantly changing the meaning of the quotes in the process. One source didn't even mention the figure she attributed to it. As if that's not bad enough, Dr Leaf also cites biased sources, pseudoscientists, and other sources that directly contradict her assertion [7; Ch 10].
This pattern of relying on mistruths and factoids to paper over the gaping cracks in her irrational assertions is repeated throughout her teaching.
The heart is a mini-brain
Dr Leaf believes that the human heart acts as a mini-brain. She states that the heart has its own thought functions, is an electrophysiological regulator of every cell in the body, and is the source of the human conscience.
Such an assertion is ludicrous, and science proves it to be so - the "still small voice" comes from our brains [8-10], and everyday office-based medical tests prove that the electromagnetic signal from the heart is too small to have any meaningful influence on our body's cells, let alone our thinking [7: Ch 11].
You control your DNA with your thoughts
Dr Leaf believes that our thinking can influence our DNA. She said this in her 2013 book [1: p35], and several times on her social media streams. The problem for Dr Leaf is that there is no credible scientific evidence that DNA is controlled by thoughts.
Her main evidence comes from a poster presentation at a 1993 psychotronics conference titled, “Local and nonlocal effects of coherent heart frequencies on conformational changes of DNA” . She describes this paper as, “An ingenuous experiment set up by the HeartMath Foundation (which) determined that genuine positive emotion, as reflected by a measure called ‘heart rate variability’, directed with intentionality towards someone actually changed the way the double helix DNA strand coils and uncoils. And this goes for both positive and negative emotions and intentions.” [1: p111]
Actually, the experiment was based on faulty assumptions, and so full of flaws in the methodology and analysis, that it could show nothing at all [7: Ch 13]. All it could prove was that Dr Leaf was so desperate to grasp hold of anything that seemed to support her theory that she was willing to use a twenty-year-old study from a group of pseudoscientists that also believe in occult practices like ESP and telekinesis (http://psychotronics.org).
On and on, the same pattern continues. She claims that our thoughts are powerful enough to control our DNA and our brain, except that the opposite is true - it's our DNA code, with some influence from our environment, that creates our pattern of neurons responsible for our stream of thoughts. She teaches that thoughts cause stress, when again, the evidence is the opposite - physiological stress is a subconscious process which changes our stream of thoughts. Dr Leaf teaches that in order to improve our mental and physical health, we need to fight any 'negative' or 'toxic' thoughts, when studies show that cognitive therapy isn't effective when compared to behavioural activation. (This is explained in more detail, and with the appropriate references, in my book ).
Dr Leaf even goes so far as to say that our thoughts can control our physical matter! [1: p33,38]
Over and over again, Dr Leaf's teaching conflicts with modern science. That Dr Leaf also regularly misquotes her sources and relies on unpublished opinion from pseudoscientists and new-age practitioners also brings her reputation as an expert scientist into disrepute.
 Leaf CM. Switch On Your Brain : The Key to Peak Happiness, Thinking, and Health. Grand Rapids, Michigan: Baker Books, 2013.
 World Health Organization. GLOBAL HEALTH ESTIMATES SUMMARY TABLES: DALYs by cause, age and sex. In: GHE_DALY_Global_2000_2011.xls, editor. Geneva, Switzerland: World Health Organization,, 2013.
 Hunter PR, MacDonald AM, Carter RC. Water supply and health. PLoS medicine 2010;7(11):e1000361.
 De Cock KM, Simone PM, Davison V, Slutsker L. The new global health. Emerging infectious diseases 2013 Aug;19(8):1192-7.
 Dickinson JA, Stankiewicz A, Popadiuk C, Pogany L, Onysko J, Miller AB. Reduced cervical cancer incidence and mortality in Canada: national data from 1932 to 2006. BMC public health 2012;12:992.
 Ronsmans C, Graham WJ, Lancet Maternal Survival Series steering g. Maternal mortality: who, when, where, and why. Lancet 2006 Sep 30;368(9542):1189-200.
 Pitt CE. Hold That Thought: Reappraising the work of Dr Caroline Leaf. 1st ed. Brisbane, Australia: Pitt Medical Trust, 2014.
 Mendez MF. The neurobiology of moral behavior: review and neuropsychiatric implications. CNS spectrums 2009 Nov;14(11):608-20.
 Zysset S, Huber O, Ferstl E, von Cramon DY. The anterior frontomedian cortex and evaluative judgment: an fMRI study. NeuroImage 2002 Apr;15(4):983-91.
 Glascher J, Adolphs R, Damasio H, et al. Lesion mapping of cognitive control and value-based decision making in the prefrontal cortex. Proceedings of the National Academy of Sciences of the United States of America 2012 Sep 4;109(36):14681-6.
 Rein G, McCraty R. Local and nonlocal effects of coherent heart frequencies on conformational changes of DNA. Proc Joint USPA/IAPR Psychotronics Conf, Milwaukee, WI; 1993; 1993.