The Nutritional Basis Of The Fetal Origins Of Adult Disease.docx

The nutritional basis of the fetal origins of adult disease 

Programming stimulus in fetal life is vital in determining the birth size and growth rate development of a fetus. This is important because several studies showed that a baby’s measurement is strongly related to chronic diseases incidence in adulthood.

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The journal proposed to look into fetal nutrition as a central stimulus for programming based on 3 evidences: 1. Manipulating nutrition on an animal’s pregnancy can produce many of the phenomena observed in epidemiological studies. 2. Small but growing direct evidences in humans that show that nutrition in maternal pregnancy can affect birth size and disease susceptibility. 3. Fetal growth in the latter part of pregnancy is mainly influence by fetal nutrient supply.

Fetal vs. Maternal Nutrition 

Fetal nutrition is mainly dependent on the transport and metabolism of the placenta rather than the maternal diet.

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There are similarities in the physiology of fetuses of different species. The fetal diet in the latter gestations of mammals are consistent in lactate, glucose, and amino acids as the major fuels for oxidative metabolism. The only difference in the different species are the proportion of these nutrients and with the time in gestation.

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Placenta’s influence in fetal nutrition via its role in metabolism: a. In sheep, placenta converts glucose to lactate b. In humans, it is important in fetal amino acid supply since all fetal glycine requirements are synthesize in the placenta c. It takes up the serine from the fetus, converts it to glycine, and released back to the fetus.

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Placenta’s influence in fetal nutrition via its metabolic demand for nutrients: a. The placenta competes with the fetus for available nutrients and the fetus also transports amino acids back to the placenta when it lacks.

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Placenta also influences fetal nutrition because it produces hormones that can influence maternal and fetal nutrition supply. It produces placental lactogen and growth hormone that contribute to maternal insulin resistance, thus increasing the availability of glucose and other nutrients.

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In sheep, the maternal undernutrition can greatly affect the fetal nutrition since the fetal glucose supply is directly related to the uterine glucose supply of the mother.

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Compared to sheep, the maternal undernutrition in humans only has a small effect on the fetal nutrition because the maternal undernutrition only has small changes in the circulating maternal blood glucose concentrations thus fetal glucose supply.

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The effect of a change in the maternal diet will vary from species to species according to the body and growth rate of the fetus.

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A small animal with a short gestation has fetuses with a high growth rate in its late gestation. These fetuses must allocate a large supply of its nutrients for growth. Because of this, limitation supply will have a greater effect on these animals than larger animals with a low growth rate.

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The fetus’ percentage of fat is directly proportional to the percentage of energy consumption directed to growth. This is because the rate of tissue acquisition will require a high energy output because of the high energy density of the fat.

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Maternal fasting may have a very different effects on fetal nutrition of a sheep and a human: a. In sheep, fasting reduces glucose supply while the lactate supply is the same b. In humans, fasting leads to maintenance of fetal glucose supply but leads to an increase of availability in fatty acids and ketones

Distinguishing birthweight from fetal growth 

It is easier to distinguish birthweight from fetal growth in animals than in human pregnancy.

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Fetal growth rate does not reflect that causal relationship it has between fetal nutrition and growth, and altered physiology.

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It is quite to assume that body proportions would be more informative since fetal growth is poorly reflected in birthweight but the evidences supporting this are excessively simplistic: a. Body proportions provide information about nutritional insults that affect the fetal growth. But measurement of fetal growth by ultrasound showed that the timing or growth pattern changes is indistinguishable. b. Fetus nutrient limitation at a certain stage can greatly affect the organs rapidly developing at that stage. But simple limitations of substrates to these organs doesn’t explain the resulting complex effects. c. Reduced abdominal circumference reflect reduced liver size. But recent findings questioned that ultrasound measurement of growth restricted fetuses show little relationship between abdominal circumference and liver size. d. Head sparing occurs as a result of blood flow redistribution in fetal life. There are evidences that showed that there is a blood flow redistribution to essential organs like the heart and brain at the expense of the organs but this is not the only mechanism in which brain growth can be maintained.

Timing and balance of nutrients 

The balance of macro- and micro- nutrients is essential in fetal growth and development.

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Most information on the balance of nutrients mostly has come from human studies.

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Even though the maternal dietary supplements showed little effect on birthweight, the supplements containing high calories provided as protein resulted in lowered mean birthweight.

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Other specific amino acids are essential in the different stages of the different organ development but this has not been explored in detail.

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Fluctuations in fetus nutrient supply can also have an important effect on fetal growth and susceptibility in disease later on.

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Intermittent exposure of a fetus to altered nutrient diets can lead to permanent changes in the brain and other developing organs.

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The role of micronutrients in fetal growth and as a potential programming stimuli has not been explored in detail. But there are some evidence of its potential importance.

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It has been revealed that there is an association between increased homocysteine levels and coronary heart disease and defects in pregnancy.

Multigenerational effects 

Other than being hereditary, nutritional influences too can have an effect on more than one generation.

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In the experimental induction of glucose intolerance in pregnant rats, it was found out that glucose tolerance was inherited but not by genetic mechanisms.

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The molecular basis of hereditary by non-genetic mechanisms may involve altered packaging and activation of various genes.

Importance: It is important to understand how fetal nutrition can affect fetal growth and development as it can be used as a programming stimulus to understand the developing chronic diseases later on. It should also always be remembered that the offspring of different species can be affected differently by its maternal and fetal diet.