Metabolism and Diet
The metabolic map above depicts the complicated
and beautifully orchestrated pathways that are involved in metabolizing, utilizing, storing,
and mobilizing stockpiled energy from our food.
When we eat a meal, it is typically a combination of carbohydrates, lipids, and protein.
Carbohydrates are found in all plant foods and they are the only source of fiber in our diets. They can be either complex (as in whole grains, legumes, and vegetables) or simple (as in refined sugars and flours). Lipids are the fats within our diet. These are found in animal products (like fatty meat, butter, lard, and dairy), in oils, and in plant fats (like avocados and olives). Dietary protein is obtained from animal products and from plant foods such as legumes, nuts, and seeds. It is also found in lesser concentrations in whole grains, vegetables, and fruit.
Our diet composition,
including which types of lipids, proteins,
and carbohydrates we choose to eat,
impacts how our food is metabolized and stored,
and which metabolic pathways are prioritized.
If eating the Standard American Diet, one high in saturated fat, refined carbohydrates, and ultra-processed foods and low in fiber and phytonutrients, de novo lipogenesis (shown in the lower left of the map above) is more likely to occur. De novo lipogenesis means the creation (genesis) of new (de novo) fats (lipids) from non-lipid sources, typically simple carbohydrates and sugars. If triggered chronically, de novo lipogenesis can result in storage of fat in the liver leading to non-alcoholic fatty liver disease and insulin resistance. Chronic elevations in de novo lipogenic pathways are also linked with a wide array of other diseases and disorders including cardiovascular disease, type 2 diabetes, numerous cancers, acne, viral infections, autoimmune diseases, neurodegenerative diseases, and dementia (Batchuluun et al., 2022).
In addition to changes in carbohydrate storage, lipid metabolism is also altered when consuming the Standard American Diet. There is a greater likelihood of consumed fat being stored in adipose tissue and our organs, rather than being burned for energy.
Our increased risk for metabolic dysfunction when eating the Standard American Diet is mediated by multiple factors:
Standard American Diet is hyper-caloric, with the majority of calories coming from foods which are calorie-rich but nutrient-poor. Our nation's reliance on hyper-caloric ultra-processed food has resulted in our population being in a state of chronic calorie surplus. Consequently, more than three quarters of American adults are overweight (30.7%), obese (42.4%), or severely obese (9.2%) (NIDDK., 2021).
The Standard American Diet is high in saturated fat from red meat, dairy, processed meats, and the saturated oils and trans fats so prevalent in processed foods. There is a greater likelihiood of fat being stored both in the liver and in adipose tissues when eating saturated fat, as compared with healthy unsaturated fats (such as the fats found in nuts, seeds, avocado, and fatty fish). Saturated fats are less prone to beta-oxidation (shown in the middle left of the metabolic map) than unsaturated fats. While oxidation may sound harmful, in this instance it means that the fats are utilized rather than being stored. Through beta-oxidation, the lipids can be converted to a molecule called Acetly-CoA and then used to create ATP (Adenosine Triphosphate), the primary energy source for our cells. Healthy unsaturated fats are preferentially oxidized (used for energy) over saturated fats, with less resultant storage both the liver and in adipose tissues (Parks et al., 2017; Flanagan, 2023).
The Standard American Diet is high in processed fructose, especially high fructose corn syrup, which is prevalent in soda, juice drinks, processed meats, sweet treats, and many fast-food items. High fructose corn syrup is particularly lipogenic and has been found to be a primary trigger of de novo lipogenesis (Geidl-Flueck & Gerber, 2023).
The Standard American Diet is high in refined carbohydrates. When there is a chronic overabundance of both calories and glucose derived from processed carbohydrates, de novo lipogenesis, fatty liver disease, and insulin resistance are all more likely.
The surplus glucose and saturated fat in the Standard American Diet contribute to increased cholesterol production in the liver. Excess cholesterol is associated with conditions such as heart disease, type 2 diabetes, metabolic syndrome, and dementia.
If we choose to instead eat a whole food, fiber-rich,
plant-predominant diet
which prioritizes healthy unsaturated fats,
such as a Mediterranean Diet,
a Whole Food, Plant-Based diet (WFPB),
or a Planetary Health Diet,
metabolic dysregulation is much less likely to occur.
Lowered risk for metabolic dysfunction when eating a whole food, plant-rich diet is promoted through a variety of factors:
Due to the focus on consumption of whole plant foods and avoidance of ultra-processed calorie-dense foodstuffs, plant-predominant diets are often lower in calories and higher in nutrients than the Standard American Diet. Being in energy balance, wherein calorie intake is equivalent to energy output, is much easier to achieve when the diet is filled with nutrient-rich foods with lower calorie density, such as vegetables, fruits, legumes, and whole grains. When all calories consumed are burned for energy needs, de novo lipogenesis is not initiated.
Whole food, plant-rich diets are devoid of the processed high fructose corn syrup that is so ubiquitous in the Standard American Diet and which seems to be a particular trigger for initiation of de novo lipogenesis.
Plant-predominant, whole food diets are also naturally lower in saturated fat due to their reduced consumption of animal products, processed meats, ultra-processed foods, and saturated oils, and they are higher in healthy unsaturated fat from plant sources such as avocados, olives (and olive oil), tofu, nuts, seeds, and fatty fish. As stated above, unsaturated fats are preferentially oxidized for energy over saturated fats, with less risk of contributing to body fat accumulations and de novo lipogenesis.
Whole food, plant-rich diets are much higher in fiber and phytonutrients than the Standard American Diet. Researchers have found that a diet rich in beneficial dietary components (such as fiber, polyphenols, Omega-3 fats, and antioxidants) reduces liver fat accumulation through the inhibition of de novo lipogenesis (Constabile et al., 2022; Green et al., 2020; Zhu et al., 2022).
The high levels of fiber in whole food, plant-predominant diets improve metabolic efficiency via the microbiome. The fiber and resistant starch in plants feed our beneficial gut microbes, which reward us by producing short-chain fatty acids. These short-chain fatty acids promote fatty acid oxidation, reduce the storage of fat in adipose tissues, shrink the size of adipose (fat) cells, and increase heat production leading to higher fat burning (He et al., 2020). In addition, the fiber in plants also slows the rate at which food is absorbed, leading to more moderate glucose elevations, reduced insulin production, and increased feelings of satiety, which aid in healthy weight management (Portincasa et al, 2022).
When the body is flooded with fiber and phytonutrients
from whole plant foods,
microbiome richness and diversity increase,
metabolic efficiency improves,
fat burning is optimized, and de novo lipogenesis and
consequent storage of fat in the liver are inhibited.
This results in reduced risk of metabolic syndrome, obesity,
fatty liver disease, insulin resistance, type 2 diabetes,
cardiovascular disease, and dementia.
In the map below, you can see the alteration in macronutrient metabolism between the Standard American Diet (SAD) (shown in the dotted pink lines), and a whole food, plant-rich diet (shown in the dotted green lines).
Protein usage is similar in both diets, with consumed protein being utilized by nearly all our cells for growth, repair, synthesis, structure, oxygen transport, energy production, and many other vital functions. Carbohydrates from both groups are utilized for immediate energy use through glycolysis and movement through the Krebs cycle to ultimately form ATP, and both diets convert extra glucose to glycogen through glycogenesis and store it in liver and muscle cells for later use. If in an anaerobic state, both diets convert pyruvate into lactate to be utilized for energy through gluconeogenesis. However, this is where metabolic processes can diverge.
As seen in the pink lines above, when eating the Standard American Diet, the chronic consumption of excess calories, processed carbohydrates, and high fructose corn syrup promotes conversion of stored glycogen first into Acetyl-CoA and then into cholesterol or into fatty acids through de novo lipogenesis. These fatty acids are stored as TAGs (triglycerides) in our adipose tissue, with potential spillover into our organs. Consumed saturated fats are less likely to be oxidized for energy use through beta-oxidation and are more likely to be stored as body fat.
As is shown in the green lines above, in a whole food, plant-rich diet which prioritizes foods with lower caloric density and avoids hyper-caloric ultra-processed foods, there is less likelihood of chronic calorie excess. Given this, during post-absorptive states (between meals or during sleep), stored glycogen is more likely to be converted back to glucose through glycogenolysis, transformed to ATP, and burned off for energy. Unsaturated fats are also preferentially oxidized through beta-oxidation and subsequently transformed to ATP for energy use, rather than being stored as fat in our adipose tissue and organs.
By increasing metabolic efficiency
and maintaining systemic energy balance,
where consumed foods are burned for energy
rather than being stored as fat,
a whole food, plant-predominant diet
facilitates weight maintenance,
encourages ongoing insulin sensitivity,
and promotes cardio-metabolic health.
As a final note, in addition to altering metabolic pathways and increasing or decreasing our disease risk, our dietary choices can also impact our gene expression. Calorie-dense, pro-inflammatory diets, such as the Standard American Diet, with high consumption of saturated fat, processed meat, and sweetened beverages have been associated with shortening of telomere length (Mierziak et al., 2021; Galiè et al, 2020). Telomeres are protective sequences of DNA at the end of our chromosomes. Their shortening is associated with aging, higher cancer incidence, and increased risk of death. Diets such as a whole food, plant-predominant diet, with high consumption of vegetables, fruits, fiber, and unsaturated fats have been shown to have a protective effect on telomere shortening or even to increase telomere length (Mierziak et al., 2021; Galiè et al, 2020).
Centering our diet around whole plant foods
reduces disease risk and helps to promote metabolic efficiency.
Whole plant foods are full of fiber, antioxidants, and healthy fats.
They are naturally lower in calories
and higher in nutrients than the foods consumed
in the Standard American Diet.
Eating a whole food, plant-predominant diet
encourages cardio-metabolic health, optimal gene expression,
and a long and healthy lifespan.
As always, wishing you excellent health and happy eating!
🌱💕
References:
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Costabile, G., Della Pepa, G., Salamone, D., Luongo, D., Naviglio, D., Brancato, V., Cavaliere, C., Salvatore, M., Cipriano, P., Vitale, M., Corrado, A., Rivellese, A. A., Annuzzi, G., & Bozzetto, L. (2022). Reduction of de novo lipogenesis mediates beneficial effects of isoenergetic diets on fatty liver: Mechanistic insights from the MEDEA randomized clinical trial. Nutrients, 14(10), 2178. www.doi.org/10.3390/nu14102178
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