Plant-based nutrition is not new. It is how humans have always eaten for the past 200,000 years. However, nutritional science has advanced dramatically in the past 20 years. First, let’s start with the facts. Certain macronutrients are known to be essential for human health. These include essential amino acids and essential fatty acids. They are essential since humans can’t make them; hence, the diet must supply them. As to why requires more explanation.
Essential amino acids were initially defined as those that were removed from the diet of rats, then animals died. But why? Proteins will only be functional with the correct amino acid sequence, and if essential amino acids are deficient in the diet, production to replace damaged protein slows down. You lose about 330 billion cells daily (1). Thus, insufficient protein production for the new cell replacement compromises future function. This lack of optimal protein replenishment would affect tissue maintenance, the immune system, and maintaining a healthy gut, as gut cells are lost at the highest rate in the body. We also know that certain amino acids (especially leucine) act as activators of gene transcription factors such as mTOR that control protein synthesis in every cell (2). Animal protein sources contain more than adequate amounts of all the essential amino acids, whereas plant protein sources are often deficient in certain essential amino acids, including leucine. This requires blending different types of plant-based protein to ensure no amino acid deficiencies.
Furthermore, the density of amino acids in plants is far lower than in animal sources, making it difficult to obtain adequate protein to maintain lean body mass even when overcoming specific essential amino acid deficiencies. Finally, you need sufficient protein to increase satiety as dietary protein stimulates the release of satiety hormones (such as GLP-1) from the gut that go directly to the hypothalamus to stop hunger (3). Vegans can achieve adequate protein by supplementing their diet with protein-rich vegetarian-based protein concentrates from soy and peas.
Can you consume too much protein? Of course, you can. The recommended safe protein consumption is between 10 and 35 percent of calorie intake (4). This corresponds to 50 and 175 grams of protein daily on a 2,000-calorie diet.
Higher levels of protein intake can produce insulin resistance by the overstimulation of mTOR, which is associated with increased cancer risk (5). On the other hand, lower levels of protein intake will not be sufficient to cause the release of satiety hormones from the gut to reach the hypothalamus to suppress hunger for approximately the next five hours. The ideal amount of protein should be about 30 grams per meal, or 90 grams of total protein daily. This amount of protein is about midway to the recommended daily intake limits (4).
What about the essential fatty acids? These fall into two classes: omega-3 and omega-6. It is only the more metabolically activated essential fatty acids (arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexenoic acid (DHA)) that are key for human health because they are the building products to produce powerful pro-inflammatory (eicosanoids) and anti-inflammatory (resolvins) hormones. To maintain health, you need a balance of both classes of hormones to fight microbial invasions, alert the immune system to the danger of external or internal injury, and, finally, promote the healing of damaged tissue (6). These metabolically activated essential fatty acids are found primarily in animal sources. Plants only contain the omega-3 precursors that are inefficiently converted into metabolically activated omega-3 fatty acids, such as EPA and DHA (7).
What about essential carbohydrates? There are none. All plants contain more than adequate (if not an excess) carbohydrates. Simple carbohydrates, such as glucose, can be synthesized from amino acids in a process known as gluconeogenesis, so they are not considered essential. This is because glucose is the primary fuel for maintaining ATP production in the mitochondria to maintain function, especially for the brain (8). Plant sources are rich in glucose as either simple sugars or complex polymers (i.e., starches) that can easily be broken down to glucose in the gut. Excess consumption of carbohydrates can give rise to hyperinsulinemia, which leads to insulin resistance (9). However, a deficiency in carbohydrate intake can also lead to insulin resistance. This is because the lack of sufficient carbohydrates (such as following a ketogenic diet) is a stress response to the lack of adequate levels of carbohydrates. Unfortunately, this stress response is mediated by increased cortisol production, increasing insulin resistance (10). Thus, you will need an appropriate balance of carbohydrates and protein to reduce insulin resistance.
You need some combination of plant and animal sources for optimal human health. But what proportion? If you are a vegan, the answer would be none. If you are a Lacto-ovo vegetarian (accounting for about 96 percent of all vegetarians) or an omnivore, you might have differing views on the proportions but not the total exclusion of animal sources. How can science help decide what the correct mix is for any individual? The answer lies in measuring your metabolic efficiency because metabolism keeps us alive, which is also the goal of nutrition.
The best general marker of metabolic efficacy is your level of insulin resistance. A simple blood test, the Homeostatic Assessment of Insulin Resistance (HOMA-IR), provides an easy measure. If HOMA-IR is less than one, your metabolism works at peak efficiency, and your diet has an appropriate balance of protein and carbohydrates. You can get further insight into your essential fatty acid requirements by looking at your AA/EPA ratio to determine if you have the correct balance of precursors of eicosanoids to resolvins to maintain inflammatory balance. Your goal is to keep that AA/EPA ratio between 1.5 and 3. As the AA/EPA ratio increases, you are more likely to develop insulin resistance as excessive inflammation drives its appearance (11). If the AA/EPA ratio is higher than 3, you either need to add more omega-3 fatty acids or reduce your intake of omega-6 fatty acids to reduce the diet-induced inflammatory burden on the body
What about athletes? Athletes will have more muscle mass to maintain than the average individual. Furthermore, they train at higher intensity levels, causing more significant muscle damage. Thus, their protein requirements will be higher for optimal physical performance. For vegan athletes, supplementing their diet with protein-rich vegetarian-based protein concentrates such as soy and peas may provide an answer. However, protein concentrates from dairy protein would provide a better choice for the athlete because of their higher levels of leucine for maximum stimulation of mTOR for protein synthesis. In addition, because of the intensity of their training, they will also require higher intakes of metabolically active omega-3 fatty acids (EPA and DHA) to reduce training-induced inflammation.
Finally, what about the environmental and ethical consequences of consuming animal protein? This is a different matter. From an ethical viewpoint, I strongly lean toward renewable sources of high-quality proteins, such as egg whites and dairy. Combined with low-glycemic carbohydrates ( primarily non-starchy vegetables and limited amounts of fruits), this will maintain an efficient metabolism that leads to a longer life by reducing diet-induced insulin resistance. To get adequate levels of long-chain omega-3 fatty acids to help control inflammation, eating fish or supplementation with EPA and DHA concentrates would be an excellent choice. For vegans, new algae-based sources of EPA and DHA are becoming available.
Although this dietary advice appears to be similar to the general outline for a Mediterranean diet, it is virtually identical to the Zone diet. Thus, the Zone diet offers superior performance to the Mediterranean diet in reducing insulin resistance (12), the goal of every science-based diet.
- Sander R and Milo R.The distribution of cellular turnover in the body. Nature Med. 2021; 27: 45-48. doi.org/10.1038/s41591-020-01182-9
- Drummond MJ and Rasmussen BB.Leucine-enriched nutrients and the regulation of mTOR signaling and human skeletal muscle protein synthesis. Curr Opin Clin Nutr Metab Care. 2008; 11: 222-226. doi: 10.1097/MCO.0b013e3282fa17fb
- Watkins JD et al.Protein- and calcium-mediated GLP-1 secretion. Adv Nutr. 2021; 12: 2540-2552. doi.org/10.1093/advances/nmab078
- Wolfe RR et al.Optimizing protein intake in adults. Adv Nutr. 2017; 8:266-275. doi: 10.3945/an.116.013821.
- Zou Z et al. mTOR signaling pathway and mTOR inhibitors in cancer. Cell Biosci. 2020; 10: 31 doi.org/10.1186/s13578-020-00396-1
- Sears B and Saha AK.Dietary control of inflammation and resolution. Front Nutr. 2021; 8:709435. doi: 10.3389/fnut.2021.709435.
- Lane KE et al. Bioavailability and conversion of plant-based sources of omega-3 fatty acids. Critical Reviews in Food Science and Nutrition. 2022; 62:18, 4982-4997. doi:10.1080/10408398.2021.1880364
- Rebelos E et al. Brain glucose metabolism in health, obesity, and cognitive decline. Journal Clin Med. 2021; 10:1532. doi.org/10.3390/jcm10071532
- Kim SH and Reaven GM.Insulin resistance and hyperinsulinemia. Diabetes Care. 2008; 31:1433-1438. doi: 10.2337/dc08-0045.
- Geer EB et al.Mechanisms of glucocorticoid-induced insulin resistance. Endocrinol Metab Clin North Am. 2014; 43:75-102. doi: 10.1016/j.ecl.2013.10.005.
- Shoelson SE et al.Inflammation and insulin resistance. J Clin Invest. 2006; 116:1793-1801. doi: 10.1172/JCI29069.
- Tettamanzi F et al. “A high protein diet is more effective in improving insulin resistance and glycemic variability compared to a Mediterranean diet. Nutrients.2021; 13:4380 doi: org/10.3390/nu13124380.