Fat is one of the essential nutrients for the human body. Firstly, it provides the energy necessary to sustain life activities. Each gram of fat can provide 37 kilojoules (9 kilocalories) of energy and can be stored as energy in the body. Lipids are the basic components of cell membranes. Fats provide the body with essential fatty acids. Additionally, fats can carry and supply fat-soluble vitamins to the body. Therefore, the human diet cannot be devoid of fats. The harms brought to the body by a high-fat diet are multifaceted, including obesity, cardiovascular diseases, and importantly, an increased risk of cancer.
Is there evidence?(a high fat diet carries a risk of cancer)
1.The American Cancer Society conducted a 13-year survey and observation of 75,000 Americans and found that individuals with more than 40% excess body weight had significantly higher rates of cancer incidence and mortality compared to the local average. Obese men mainly died from colon cancer, rectal cancer, and prostate cancer, while women mainly died from breast cancer, endometrial cancer, cervical cancer, gallbladder cancer, and bile duct cancer. The leading causes of cancer mortality in the United States are lung cancer, colon cancer, breast cancer, and prostate cancer. Apart from lung cancer, which is related to but not primarily caused by a high fat diet, the other three cancers have a close relationship with a high fat diet.
2.The Japanese diet contains half the fat calories of the American diet, and correspondingly, the incidence rates of breast cancer and colon cancer in Japan are much lower than those in the United States. To demonstrate that the differences in cancer incidence rates are not due to race or genetics but rather to lifestyle, experts investigated the breast cancer and colon cancer incidence rates of Japanese individuals who had lived in the United States for 20 years and adopted a “Westernized” lifestyle, finding that they were not significantly different from those of local Americans.
3.Breast cancer is a malignant tumor that seriously endangers women’s health and lives, with an incidence rate of 1% among adult women and ranking first in female cancer mortality. The highest incidence of breast cancer occurs in middle-aged women aged 40-60, accounting for 75% of cases. The incidence and mortality rates of breast cancer are closely related to a country’s residents’ standard of living, which naturally includes fat intake.
For example, the breast cancer mortality rate among white Americans is 5.9 times higher than that among Japanese individuals. The fat daily intake and breast cancer mortality rates among residents of different countries are as follows: Thailand 24g, 1/100,000; Japan 41g, 4/100,000; Mexico 60g, 5/100,000; Romania 68g, 10/100,000; Italy 83g, 18/100,000; United Kingdom 148g, Netherlands 146g, Denmark 158g, all exceeding 25/100,000. The positive correlation between the two is evident from the above numbers.
4.Renal cancer: The National Cancer Institute of the United States studied the health records of 360,000 Swedish men, among whom 895 developed renal cancer. An analysis of the relationship between body weight and renal cancer risk revealed that the risk of developing renal cancer was twice as high for obese individuals.
5.Prostate cancer: An international survey indicated a close relationship between fat intake and prostate cancer mortality rates. Since 1950, the fat content in the Japanese diet has been increasing, leading to a rise in the incidence and mortality rates of prostate cancer. A research group in the United States also found a close relationship between fat intake and the incidence and mortality rates of prostate cancer.
6.Lung cancer: Smoking is a well-known cause of lung cancer, but it is not the only cause. Dr. Alan Fange from the National Cancer Institute of the United States analyzed the health conditions of 2,000 non-smoking women, including 600 with lung cancer. The conclusion drawn was that women with a high-fat diet (where fat accounts for over 40% of total calorie intake) had a five times higher incidence of lung cancer than the general population (where fat accounts for less than 30% of total calorie intake).
7.Types of fats: According to fatty acid content, fats are classified into saturated fats, monounsaturated fats, and polyunsaturated fats, all of which are related to cancer occurrence. However, saturated fats (mainly animal fats) have the strongest carcinogenic effect on colon cancer. Western countries with high meat consumption also have high rates of colon cancer.
8.Unsaturated fats: Given the clear relationship between saturated fats and colon cancer incidence rates, unsaturated fats must be much safer, right? Not necessarily, as they simply promote different types of cancer. Animal experiments have shown that when 60 rats were divided into two groups and fed corn oil and heated butter for 40 months, all rats fed corn oil developed tumors, while none of those fed butter did. An animal experiment on various oils clearly demonstrated that the carcinogenic effect of vegetable oils (excluding coconut oil, which is a saturated fat) is stronger than that of animal fats.
However, some research suggests that a low fat diet does not help reduce the risk of cancer. According to a report published in the Journal of the American Medical Association, the National Institutes of Health conducted an 8-year study on the diets of 49,000 women aged 50-79 and found no significant difference in the risk of developing breast cancer, heart disease, or stroke between those on a low-fat diet and those who did not restrict their diets as usual.
Carcinogenic Mechanisms of high fat diet
1.Is Estrogen a “Carcinogenic Culprit”?
To clarify the causes of breast cancer, a medical center in Boston, USA, studied the relationship between the lifestyles of 20 women and their estrogen levels. Among these women, 10 consumed a diet of only vegetables, milk, and eggs, while the other 10 ate meat, fish, and vegetables. It was determined that the latter group consumed 20% more fat than the former, who in turn consumed 10% more dietary fiber.
Further analysis of the estrogen content in the blood, urine, and feces of the two groups revealed that vegetarians had lower levels of estrogen in their blood and urine, but more than double the amount of estrogen in their feces compared to meat-eaters.
This study clearly demonstrated two facts: firstly, high fat diet is the main reason for increased estrogen in the blood and urine, and secondly, dietary fiber is the main reason for reducing estrogen in the blood and urine and increasing its content in feces.
Researchers have found that daily caloric intake affects hormone levels in the body, especially estrogen levels. Analysis of saliva from women in Bolivia, the Democratic Republic of the Congo, Nepal, Poland, and the USA showed that the content of estrogen and progesterone in saliva is positively correlated with daily caloric intake and also with the incidence rate of breast cancer. The incidence rate of breast cancer among American women is almost double that of Congolese women, as their daily caloric intake is about twice that of Congolese women, with their saliva progesterone levels about 10% higher than those of Congolese women.
Given the close relationship between daily caloric intake and the incidence rate of breast cancer, could dieting reduce the risk of breast cancer? Professor Grazyna Jasińska of the Public Health Research Institute at Jagiellonian University in Poland wrote in the American Medical Journal, “Changing women’s lifestyles may reduce the likelihood of breast cancer.” Dieting to reduce the risk of breast cancer “is a logical conclusion. Dieters will reduce the levels of estrogen and progesterone in their bodies, and women who have gained several kilograms after their twenties will have an increased risk of breast cancer after menopause.
Hormone levels, especially estrogen and progesterone, are of great significance to women’s health. Normally, these two hormones are in relative balance. If this balance is disrupted, an absolute or relative excess of estrogen can cause physiological chaos, leading to excessive proliferation of breast epithelial cells and increasing the risk of malignancy. Estrogen includes estrone, estradiol, and estriol. In adult women, the main form of estrogen is estradiol, which is twice as abundant and ten times as potent as estrone. Estriol is merely a metabolite of the other three estrogens and has lower potency.
2.Fat(high fat diet) Promotes the Formation of Estrone:
Adipose tissue in the human body converts androstenedione, a corticosteroid from the adrenal cortex, into estrone. High levels of estrone in the body can induce prostate cancer. Both saturated and unsaturated fatty acids in fats stimulate the growth of prostate cancer.
3.high fat diet Promotes the Secretion of Bile Acids and Bile Salts:
Bile acids generally combine with potassium and sodium to form bile salts. Bile salts promote the emulsification of fats into fat droplets, reducing surface tension and increasing surface area, facilitating contact between pancreatic lipase and fats, thus accelerating fat breakdown.
At the same time, bile salts activate pancreatic lipase, increasing its activity, and thus promoting fat breakdown. Fats promote the secretion of bile acids in the liver and the formation of bile salts, especially saturated fats. Normally, a large number of bacteria live in the intestines, including aerobic and anaerobic bacteria. One type of anaerobic bacteria metabolizes bile acids to produce deoxycholic acid and lithocholic acid, with deoxycholic acid transforming into the highly carcinogenic methylcholanthrene. Fatty acids fermenting in the intestines also produce carcinogenic peroxides.
Bile acids themselves can damage the intestinal wall and induce tumor cell growth. This is the mechanism by which a high-fat diet induces colon and rectal cancer. Epidemiological studies also show that feces from patients with colon cancer contain high levels of bile acids and other mutagenic substances, while the opposite is true for populations with low rates of colon cancer.
Recent studies have found that high levels of bile acids are not only a cause of colon and rectal cancer but also of small intestine adenocarcinoma and even stomach and esophageal cancer. It is not difficult to understand how bile acids can cause cancer in the large and small intestines because bile acids come into contact with the walls of the small and large intestines as they move down the digestive tract with food.
However, why can bile acids also affect the walls of the stomach and even the esophagus? Although the stomach has two “gates” (referring to the cardia between the stomach and esophagus and the pylorus between the stomach and duodenum), the concentration of bile acids in the stomach is significantly higher in people who have undergone gastric resection surgery than in healthy individuals. Bile acids cause damage to the gastric mucosa, and the risk of gastric cancer is positively correlated with the concentration of bile acids in the stomach. Mice subjected to bile duct diversion into the stomach surgery developed gastric cancer. Bile acids enhance the carcinogenic activity of N-methyl-N’-nitro-N-nitrosoguanidine.
Although the cardia and pylorus serve as “gates” to prevent food reflux, there are times when these “gates” fail. Eighty-five percent of patients with reflux esophagitis have bile acids in their stomach fluid, with concentrations 6-8 times higher than those of controls. Studies have shown that people who have had their gallbladder removed have an increased risk of esophageal adenocarcinoma. Animal experiments have found that artificially creating a reflux model in rats involving the duodenum, stomach, and esophagus can induce esophageal adenocarcinoma in rats. This demonstrates that bile acid reflux from the duodenum is closely related to the occurrence of gastric and esophageal adenocarcinoma.
Primary bile acids include cholic acid and chenodeoxycholic acid, which are produced in the liver from cholesterol and then conjugated with glycine or taurine before entering the gallbladder. After entering the digestive tract, they are deconjugated from glycine and taurine, with a portion being absorbed into the bloodstream and another portion being deoxygenated by bacteria into secondary bile acids. Secondary bile acids include deoxycholic acid and lithocholic acid. Recent studies have focused on the carcinogenic effects of deoxycholic acid among secondary bile acids, while lithocholic acid is believed to have some anticancer effects.
4.The Carcinogenic Mechanism of Unsaturated Fatty Acids:
Due to the presence of double and triple bonds in their long carbon atom chains, unsaturated fatty acids are easily oxidized, producing chemically active substances, including free radicals and lipid peroxides, which can induce cellular carcinogenesis.
5.A high fat diet, especially excessive intake of unsaturated fats, can lead to a deficiency in vitamin E, which is beneficial for enhancing the body’s anticancer capacity.
6.A high fat diet can accelerate the excretion of magnesium, an element with anticancer properties.
Fat Intake Should Be Moderate.
Fat is an essential nutrient for the human body and an indispensable substance, but high fat diet may pose a certain cancer risk. Therefore, intake should be moderate to meet the metabolic needs of the body without increasing the risk of cancer.
1.Types:
Fat is composed of fatty acids and glycerol. Fatty acids can be divided into saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids. For the human body, the best ratio of these three types of fatty acids is 1:1:1.
2.What Constitutes a Moderate Amount?
In 1977, the U.S. Senate Committee on Nutrition and Human Needs suggested reducing the fat intake of Americans, from 40% of total daily energy intake to 30%. What does 40% of total daily energy intake amount to? Assuming a total daily energy intake of 10,050 kilojoules (approximately 2,402 kilocalories), 40% would be about 4,020 kilojoules (approximately 960 kilocalories), equivalent to about 107 grams of fat, more than 3kg per month. Reducing it to 30% of total daily energy intake would mean consuming about 80 grams of fat per day, approximately 2.4kg per month.
Calculating daily fat intake should not only include the cooking oil consumed by the family each month but also animal fats and fats ingested through other foods. In terms of animal foods, do not assume that lean pork, beef, lamb, chicken, and duck do not contain fat; these foods often contain some amount of fat. Other foods, including snacks and meals eaten at work or school cafeterias, should also be estimated.
Nutritional associations recommend that daily fat intake should ideally account for 20% to 25% of total daily energy intake. If calculated based on a total daily energy intake of 10,050 kilojoules (approximately 2,402 kilocalories), this would equate to 2,010 to 2,512 kilojoules (480 to 600 kilocalories), or 53 to 67 grams of fat. The World Health Organization recommends that daily fat intake should not exceed 30% of total energy.