The “Al-Tayyibat” system by the Egyptian doctor Diaa Al-Awadi has sparked widespread controversy about its health effectiveness, as it is based on two lists: One includes what is permitted and the other what is prohibited. It is claimed that many common foods harm the intestines and cause indigestion, which opens the door to other diseases.
The prohibited list includes foods that people used to consider beneficial, such as eggs, chicken, leafy vegetables, cucumbers, and tea, which prompted many to try the system themselves to verify the validity of these claims.
What do scientific studies say about these foods? Has it actually been proven that any of them are harmful to the body’s health?
First: eggs
Eggs are one of the richest sources of high-quality protein and contain vitamins, minerals, unsaturated fatty acids, cholines and carotenoids.
Despite its documented benefits in supporting immunity, building muscle, fighting tumors, and helping to control weight, its full health effects are still up for debate.
Eggs are associated with some warnings of heart and arterial problems due to their 200 mg cholesterol content in each average egg, in addition to studies linking them to an increased risk of metabolic disorders, immune diseases, and cancer.
Why are eggs associated with certain risks?
Eggs contain abundant amounts of choline, which gut bacteria convert into trimethylamine (TMA), then undergoes a series of reactions that end up stimulating the production of trimethylamine oxide (TMAO) in the liver, a biomarker linked to cardiovascular disease.
Researchers have hypothesized that excessive egg intake may affect the composition of the intestinal microbiome and increase the production of this compound, but this relationship has not yet been proven and requires further research.
Eggs in studies
- Egg consumption and high risk of death:
A Chinese meta-analysis published in 2022 in The Journal of Nutrition and Disease observed a linear relationship between high egg consumption and the risk of death from all causes.
An additional egg per day has been linked to an increased risk, especially for women, and an increased risk of death from heart disease has been observed in those over sixty.
However, the study did not prove direct causality, and was marred by methodological limitations such as reliance on self-reporting, lack of knowledge of how to prepare eggs, and lack of monitoring of the participants’ diets.
- Eggs and gastrointestinal tumors:
Regarding the relationship of eggs to the digestive system specifically, Australian researchers conducted a meta-analysis published in 2014 in the European Journal of Nutrition, which included 7 cohort studies (Cohort) and 37 case-control studies (Case-Control), with a total of 424,867 participants and 18,852 cases with gastrointestinal tumors.
The research concluded that there is an association between egg consumption and the development of gastrointestinal tumors, especially colon cancer, with an increase of approximately 29%, without proving direct causality.
- Eggs and gut health:
Later in 2025, Australian researchers published a systematic review in the journal Nutrients evaluating the effect of eggs on digestive health across indicators such as the gut microbiome, inflammatory markers, and TMAO levels.
The results varied, and the effect of eggs on the microbiome was not clear, noting that the reviewed studies did not make eggs a main target, but rather focused on general dietary patterns, which limits the possibility of isolating the effect of eggs specifically on the health of the digestive system.
- Eggs and the microbiome:
As for direct intervention experiments, in 2021, Chinese researchers published in the Journal of Food Science & Nutrition the results of an experiment on 12 male volunteers who ate two boiled eggs daily for two weeks.
The experiment showed that the composition of the intestinal microbiome was not affected, but positive changes occurred in the metabolic functions of intestinal bacteria. However, the small sample and short duration of the experiment limit the possibility of generalizing the results.
Therefore, the relationship between eggs and digestive system health remains inconclusive, and the prevailing recommendation is to eat them in moderation until stronger evidence becomes available.
Second: chicken
Chicken is considered one of the most consumed sources of animal protein around the world, and dietary guidelines recommend eating 100 grams of it one to three times a week.
Despite its popularity, some researchers have begun to warn against excessive use of it, which is consistent with the position of the Tayibat system, which prohibits it completely on the grounds that it hinders the digestion process.
Chickens in studies
- Poultry and the risk of death
In 2025, Italian researchers published in the journal Nutrients the results of a follow-up study that spanned about 19 years on 4,869 people between the ages of 30 and 50 years.
The study revealed that eating more than 300 grams of poultry per week increases the risk of death by 27% compared to those whose consumption does not exceed 100 grams per week.
The highest death rate from stomach and intestinal cancer was also recorded in the group that consumed the most. However, the study has methodological limitations, most notably the lack of knowledge of the source of the poultry and whether it is fresh or processed.
- Microplastics in poultry
From a different angle, in 2026, researchers from Bangladesh reviewed in the journal Poultry Science a possible aspect of the relationship between poultry meat and human health, hypothesizing that exposure of poultry to microplastics through food, water, or breeding tools may lead to their accumulation in their organs and then their transmission to humans upon consumption.
They noted that this may be linked to increased inflammation, oxidative stress, and disruption of digestive system functions and metabolic processes. However, these results are still hypothetical and require more long-term studies to verify them.
- Poultry and antibiotics
In a related context, researchers from India, America, and Australia warned in a study published in 2019 in the Indian Journal of Microbiology that the excessive use of antibiotics and modified feeds in raising poultry disrupts the microbiome of its intestines and produces resistant bacterial strains, which may negatively affect the health of the human digestive system when ingested.
- Poultry and heavy metals
As for heavy metals, in 2023, researchers from Bangladesh observed in the journal Plos One that concentrations of lead, cadmium, chromium, and arsenic exceeded the permissible limits in some parts of chicken meat, and it is likely that they come from feed. However, the risk assessment index showed that it was still within acceptable limits and did not pose a significant cancer risk, according to the study.
- Scientific evaluation of poultry
On a broader level, specialists from Purdue University conducted a scoping review that included 525 studies and was published in 2022 in the journal Advances in Nutrition, concluding that the available evidence is insufficient to independently evaluate poultry as a healthy or unhealthy food, as only 1% of studies dealt with processed poultry.
It also turned out that most research compared poultry to other foods without studying it as a separate factor, which requires conducting independent experimental studies to evaluate its real impact on human health, especially the digestive system.
Third: leafy vegetables
Green leafy vegetables have historically been associated with abundant health benefits as they are rich in vitamins, minerals, and fiber. The World Health Organization has recommended eating at least 400 grams of vegetables and fruits daily. But the Tayyibat system claims that it may play a negative role on health, so what do the studies say?
Leafy vegetables in studies
- Leafy vegetables and toxic metals
Spanish researchers evaluated the toxicity of leafy vegetables by analyzing 47 toxic nutrients in the diet of Canary Islanders, and published their results in 2023 in the journal Toxics.
They found that leafy vegetables are a good source of iron, manganese, zinc, selenium, and others, and that the highest content of toxic metals such as cadmium, arsenic, and lead was found in spinach, arugula, cress, and Swiss chard.
However, consuming normal quantities of it was not associated with any toxicity among the participants, while high levels of toxic thallium were observed among its frequent consumers, which requires further studies to monitor the safety of its consumption.
- Health benefits of leafy vegetables
On the other hand, most published studies show the benefits of leafy vegetables and do not indicate documented, generalizable digestive harms.
Researchers from Thailand and Australia revealed in Nature magazine in 2025 that it is rich in antioxidants that slow the digestion of carbohydrates and reduce the rate of fat digestion.
American specialists also concluded in the magazine Nutrients in 2021 that eating it reduces indicators of inflammation and DNA damage, and that increasing its consumption may reduce the risk of colon cancer.
Many studies point to the noticeable lack of studies that have dealt with the direct relationship of leafy vegetables with the health of the digestive system and how the body responds to it, and many of them have recommended the need to continue research to fill this gap and uncover its potential risks, if they exist.
Fourth: Option
Cucumber is known to be rich in water and low in calories, and has a long history in traditional Indian medicine as an antioxidant and anti-inflammatory. Contrary to what the Tayibat system claims that it is difficult to digest, studies indicate the opposite.
Choice in studies
Indian researchers revealed in 2012 that the aqueous extract of cucumber pulp showed intestinal laxative properties and increased the rate of stool excretion in laboratory rats, indicating a digestive advantage, although the experiment was limited to the animal model and needed to be supported by clinical studies on humans.
A study published in 2021 in the Journal of Pharmaceutical Biology also demonstrated that cucumber increases colon muscle contraction and enhances the secretion of fluids within the intestines, which contributes to alleviating constipation.
A review published in 2012 also pointed out the historical use of cucumber seeds in the prevention of constipation, while noting the scarcity of sufficient scientific evidence about its therapeutic properties.
On the other hand, in 2022, researchers from Jordan, Pakistan, and Thailand reached a different result, as they found that cucumber seed extracts possess anti-diarrheal and anti-spasmodic properties by regulating smooth muscle contraction via calcium channels in laboratory studies and animal models, which means that cucumber may benefit the digestive system, but through multiple and disparate mechanisms. These results, in turn, require further clinical studies to confirm their effectiveness in humans.
Most of the published studies urge that more experiments be conducted to confirm the effectiveness of cucumber on human cells, and the recommendation for its safety remains in place until the opposite is proven through long-term scientific experiments.
Fifth: Tea
Tea is one of the most popular beverages around the world, and fully brewed black tea tops the list of its varieties with a production rate of 78%. Although it is included in the list of prohibited things in the Al-Tayyibat system, claiming that it causes constipation, studies say the opposite.
Tea contains polyphenols as one of its most prominent bioactive compounds, and their positive effect has been indicated in stimulating the growth of beneficial bacteria in the intestines and inhibiting some types of harmful bacteria.
Tea in studies
Researchers from various Chinese research centers and universities conducted an experiment, the results of which they published in 2023, in which it was found that drinking black tea regularly reduces constipation by improving bowel movement and regulating water absorption, and this effect was more evident in aged types of black tea.
However, the experiment was limited to laboratory mice and did not include humans, which requires completing it with clinical studies to confirm its results.
On the other hand, a cross-sectional study published in 2024 in the journal BMC Public Health examined the effect of caffeine on constipation, taking into account that black tea contains between 1.5% and 3% of caffeine.
The results showed a clear link between increased consumption of foods and drinks rich in caffeine and a lower incidence of constipation. The study even went so far as to recommend that those suffering from constipation continue to drink tea, coffee, and chocolate bars to get rid of it.
However, the small sample size and its limitation to adults from the United States limit the generalizability of these findings more broadly.
As for researchers from India, they conducted laboratory experiments on models of mice to test the effect of black tea extract on intestinal movement, and their results revealed that the thearubigin compounds found in tea, which are responsible for its distinctive dark color, played a pivotal role in enhancing intestinal movement and accelerating the passage of food through it.
Most recent studies agree that tea may be linked to improving bowel movement and alleviating constipation, not worsening it, which is in direct contradiction to what the Tayibat system claims.
However, there remains a need for more clinical studies on humans to confirm these results and determine the extent of the actual effect of tea on the digestive system.
