To eat meat or not eat meat, that is the question of concern for many. Documentaries like The Game Changers and Forks Over Knives have helped to popularize vegetarian and vegan lifestyles and cast doubt on those who choose the omnivore lifestyle. But is the demonizing of meat justified? You likely already have an opinion, but let’s look at the science.
Correlation vs. causation
To properly understand scientific research, especially regarding nutrition, it is critical to differentiate between observational research and randomized controlled trials. The majority of nutrition science is considered nutritional epidemiology which leans on observational research. Essentially, this means researchers look at a large group of individuals, track innumerous habits, diet choices, etc. and attempt to find (aka, observe) an association between factors and diseases/conditions to determine a cause. Unfortunately, nutritional epidemiology cannot in fact determine causation and only provides weak data from which to derive recommendations (though it is often helpful in leading to more robust research and trials in the future).
Potential meat cons
Carcinogens are substances that have been shown to increase cancer risk. When meat is cooked at high temperatures, heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are formed. In addition, animal studies show heme iron-rich red meat is toxic to living cells. Meal components and nutrients however change how these chemicals affect health. One 2021 randomized, controlled trial found that just 1 cup of cooked leafy greens a day helped to offset colon cell damage and inflammation from red meat intake. Many public health authorities such as the International Agency for Research on Cancer (IARC) have relied on mostly observational data (over 800 epidemiological studies) to determine recommendations. Still, the World Health Organization's (WHO) IARC reports that there is limited evidence that red meat (I.e. beef, pork, lamb) consumption is associated with colorectal cancer, whereas processed meat causes colorectal cancer. The WHO, World Cancer Research Fund, Harvard School of Public Health, and the 2015-2020 Guidelines for Americans recommend limiting red meat, whether processed or unprocessed, but not other types of meat.
Low in nutrient density
While meat is dense in some nutrients such as B12 and protein, it lacks other health-promoting nutrients such as antioxidants, cancer-preventing phytochemicals and gut-supporting fiber found in plants. A 2021 randomized controlled feeding-trial found that participants who ate fried meat four times a week for four weeks experienced negatively altered microbiome diversity, worsened glucose management and inflammation.
High in saturated fat
Saturated fat is a type of fat that may need to be reduced by some at-risk populations. Red meat often contains more saturated fat than poultry or seafood which may be detrimental for those at risk for or have already been diagnosed with cardiovascular disease, diabetes, and/or Alzheimer’s disease. One randomized, controlled trial found that when saturated fat was kept low vs. high, white meat such as poultry was not superior to red meat as far as cardiovascular disease risk (this study did not assess cancer risk).
Potential meat pros
The International Protein Board recommends protein intake above the Recommended Dietary Allowance (RDA) of 0.8g/kg (a minimum to prevent protein deficiency). Recommendations range from 1.1 to 1.8g/kg (0.5-0.8 g/lb) body weight for most adults (excluding some athletes who may need more). This range includes those seeking to build or preserve muscle mass while losing weight and aging.
Satiety & weight
Managing calorie intake is a key factor in managing weight. Protein is the macronutrient most responsible for satiety and delayed onset of hunger after meal intake, as well as helping to preserve muscle mass during the weight loss and aging processes. Since obesity is a worldwide epidemic, boosted protein intake through meat consumption may increase weight loss and outweigh potential risks, as well as provide more meal and diet satisfaction, despite less calories.
Vitamin B12 is an essential (required) water-soluble vitamin that your body cannot make internally. Adequate B12 intake has numerous important benefits such as helping to form red blood cells, lower inflammation, reduce risk of depression, protect brain cells, improve energy production, and ensure healthy nerve function. Nearly every type of meat, seafood, egg and dairy product is rich in B12, as well as some vegetarian sources such as fortified nutritional yeast and fortified non-dairy milk.
Leucine is the essential amino acid required for muscle synthesis after exercise. When leucine intake is low, muscle mass growth and maintenance may be compromised. Whole food sources rich in leucine, reported by the USDA FoodData Central database, that provide more than 1000mg per serving are listed below:
- Chicken, cooked, chopped/diced - 2000mg per 3 ounces
- Beef, cooked – 1820mg per 3 ounces
- Turkey, cooked – 1710mg per 3 ounces
- Navy beans, canned – 1670mg per cup
- Salmon, wild Atlantic, cooked – 1370mg per 3 ounces
- Lentils, cooked – 1300mg per cup
- Yogurt, Greek - 1211mg per cup
- Cottage cheese, 2% low fat – 1185mg per ½ cup
- Almonds, whole – 1050mg per ½ cup
To help clarify the epidemiology-based red meat concerns with a more robust scientific approach, the Annals of Internal Medicine published 6 papers by investigators within the Nutritional Recommendations and accessible Evidence summaries Composed of Systematic reviews (NutriRECS) group. The goal of these papers was to assess how both unprocessed and processed red meat affect the risk of cardiovascular disease, cancer and all-cause mortality. The first paper summarized the group’s recommendations – adults can continue to eat meat at their current intake levels stating that current evidence (mostly observational) was too weak to recommend limiting intake.
For accurate and dependable population-wide recommendations, strong evidence from randomized controlled trials and mechanistic studies rather than primarily observational data or personal experience is key. Future research may elucidate different findings, but for now it appears red meat intake as part of a healthy omnivore diet (not the risky Standard American “high meat and sugar, low vegetable” Diet) does not generally worsen health. In fact, it may increase specific nutrient intake, and improve muscle mass, weight loss and body composition by helping meet protein needs. For those with high risk of colorectal cancer or those who prefer to be extra cautious, it appears prudent to limit processed meat and saturated fat, reduce intake of grilled or barbecued meat, and serve meat with antioxidant and fiber-rich vegetables.
We all tend to have personal nutrition biases because we eat multiple times a day, every day. But what works for you may not work for others, and vice-versa. Work with a dietitian to help you personalize your diet and lifestyle to meet your health goals, including your meat intake.