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Is food triggering brain fog, low mood & lethargy? And our collaboration with YorkTest

Have you ever wondered if what you eat has anything to do with your mood, energy levels and ability to concentrate? Do you ever experience ‘brain fog’ and tiredness and wonder why you feel anxious and low when others seem to cope?

 New research is showing that what happens in your gut after eating food has a direct effect on your brain and how you feel. Simple diet changes can have profound effects. Stephanie, a 28-year-old lawyer, is a case in point. “After a week the brain fog and tiredness were significantly better and then after a few weeks, all of my symptoms had gone!” Wanita , age 41, who was signed off work, had complete relief from her anxiety and fatigue and she was then able to return back. Her doctor had recommended anti-depressants. Nicola, age 51, had constantly felt tired and lethargic, with brain fog and the inability to concentrate. “If I didn’t eat regularly, I felt worse, so I was constantly grazing on food. I know now I was eating the wrong foods which didn’t help”. Now she says “I feel so much better in myself and have a lot more energy. The best thing is to not have brain fog.

“The best thing is to not have brain fog.”

What they all had in common were specific food intolerances whereby their gut and immune system reacted, creating a kind of inflammation and reactivity that can both cause gut issues such as IBS, pain and bloating, but also psychological issues such as brain fog, anxiety and depression. The ability of foods to trigger mental health issues has been known for a remarkably long time. Back in 1980 Dr Joseph Egger, writing in the Lancet medical journal (1) reported: “The results showed that allergies alone, not placebos, were able to produce the following symptoms: severe depression, nervousness, feeling of anger without a particular object, loss of motivation and severe mental blankness.” But why certain foods in certain people could produce mood changes and brain fog wasn’t known.

Researchers in the US (2) China (3), Poland (4) and the UK (5) have found out why and it’s all to do with ‘food intolerance’ that is unique to the individual. While classic allergies cause the body to product IgE antibodies that attack the offending allergen, depression, brain fog and even schizophrenia, according to research at Johns Hopkins University School of Medicine in the US, can occur when a person’s immune system produces a different kind of ‘IgG’ antibody that attacks their offending foods. 

What Stephanie, Wanita and Nicola had in common is they are part of research that has involved thousands of people, all having an IgG food intolerance test administered via a home test kit provided by YorkTest, and then avoided their ‘reactive’ foods. 

Scientific Director at YorkTest, Dr Gill Hart, says “YorkTest pioneered food IgG testing developing our first food intolerance test back in 1998 in collaboration with scientists from the University of York. Since then, YorkTest has provided over half a million tests. The tests are accurate, have been shown to be effective and have demonstrated >98% reproducibility. For those with high food IgG reactivity, the pattern of IgG trigger foods is unique to each individual. The tests provide valuable information, and with nutritional advice provided as part of the Food Intolerance Test, people feel fully supported in making the required dietary changes. The good news is that food intolerances aren’t necessarily for life, and those taking the test and changing their diet have reported improvements over a relatively short period of time”. 

Unlike conventional IgE allergies, which can last for life, IgG antibodies “die off” so, theoretically, if you avoid the offending food for at least three months, you may be able to reintroduce the food without reacting. However, it is worth doing this systematically because some people do continue to react.

Nine in ten people having the test, and avoiding their offending foods report improvement in mood, brain fog and lethargy (5). See the table below for reported results from YorkTest’s research.

YorkTest are a supporter of Food for the Brain and offer our Friends £10 off the price of a test in the UK. If you live in the UK go to and enter the discount code FFB10 in the basket.

If you live in the US go to and enter FFB10US in the basket for your $10 discount. YorkTest will match your discount with a donation to Food for the Brain to help us help more people regain mental health through optimum nutrition.

Symptoms (3026 Subjects)Moderate benefit %High benefit %Total %Low or no benefit %

Anxiety (40)
Behavioural problems (3)
Autism (1)
Depression (79)
Fatigue (436)
Hyperactivity (3)
Lethargy (212)
Mental fog (24)
Nausea (61)
Panic attacks (15)
Tension (9)
Insomnia (12)
Bad moods (15)

Unpublished data reproduced with permission from the study published as Hardman G and Hart G, 2007: Dietary advice based on food-specific IgG results. Nutrition and Food Science 37, 16-23


1. Egger J et al, The Lancet 865-869, October 15, 1980

2.. Severance E et al (2015) IgG dynamics of dietary antigens point to cerebrospinal fluid barrier or flow dysfunction in first-episode schizophrenia. Brain Behav Immun. 44:148–58  

3. Tao R et al (2019) Chronic Food Antigen-specific IgG-mediated Hypersensitivity Reaction as A Risk Factor for Adolescent Depressive Disorder. Genomics Proteomics Bioinformatics 17(2):183-189.

4. Karakuła-Juchnowicz H et al (2017) The role of IgG hypersensitivity in the pathogenesis and therapy of depressive disorders. Nutr Neurosci 20:110-8; see also Karakula-Juchnowicz H et al (2018) The Food-Specific Serum IgG Reactivity in Major Depressive Disorder Patients, Irritable Bowel Syndrome Patients and Healthy Controls. Nutrients 10:548

5. Hart G (2017) Food-specific IgG guided elimination diet; a role in mental health? BAOJ Nutrition 3:3:033  

6.  Hardman G and Hart G, 2007: Dietary advice based on food-specific IgG results. Nutrition and Food Science 37, 16-23