it recycles nutrients
Too little energy or too few nutrients are consumed over time, causing insignificant weight loss or a nutrient deficiency disease. Nutrition stores in the body that are depleting. Below the body's nutrient needs.
Acetone cannot kill you unless consumed in excessive amounts. That doesn't mean it is a safe substance. Acetone should be avoided due to the vapors causing minor symptoms and possible long term affects.
An enhanced (or accelerated) greenhouse effect which is causing global warming.
microorganisms can harm animals by infecting them, releasing toxins inside of animals when consumed, or causing malnutrition.
If your heart stops, your blood flow will stop causing a stop to the nutrients entering your organs and your organs will not get oxygen causing you to die.
Alcohol is a notorious culprit of causing nausea and vomiting. This is even more-so when alcohol is over-consumed.
Diarrhea may sweep other nutrients out of the intestine before they can be absorbed, causing malnutrition.
Need a list of groups you'd have in mind. Offhand, ELF (Earth Liberation Front) would probably be the most likely contender. Because, you know, nothing says "save the earth" like torching it, causing massive amounts of fuel and water to be consumed fighting the fire, and causing chemical runoff from the firefighting operation to seep into the ground and stormwater drains in the vicinity of the fire.
All three macro nutrients - fats, carbohydrates, and proteins can and are converted to stored fat. Many protein supplements claim that "excess" protein just passes through and a fair amount does - while causing excess work and potential harm to the liver and kidneys. Across the board though all of the three main macro nutrients can be converted by the liver for storage in fat cells.