To my knowledge the body must have it's 'main' source of energy as either fat(ketosis) or carbohydrates.

However I was wondering if it could be done with protein alone(e.g. fat boiled out of meat). If not what if you also ate 'low calorie green vegetables e.g. kale or spinach. Obviously you could not get enough calories from low calories vegetables but would it allow you to gain weight whilst using protein(without fat) as the main source of calories?


  • You'll rapidly lose weight. Commented May 24, 2016 at 18:08
  • This has been asked so many times that there is really no need for a formal answer, to be honest. If you eat above your body's calorific needs then you will put on weight. If you don't, then you will lose weight. When your body no longer has any use for the protein (Broken down) beyond, being used as a building block, it's converted into glucose for energy. There's nothing more major, to it. The only variables to consider are medical conditions that may predispose you to weight gain or loss or those that affect normal bodily function.
    – user19679
    Commented May 26, 2016 at 19:01

2 Answers 2


Going on such a diet (one that is void of fat) for sustained periods of time is simply not possible. Fat is an essential macronutrient your body needs. Never go on a diet that is void of fat.

  • Fat is mandatory for the digestion and absorption of fat soluble micro nutrients (Vitamin A, D, E, and K).
  • Fats are also sources of EFAs (Essential Fatty Acids).
  • EFAs play an important role in the life and death of cardiac cells.
  • EFA deficiency results in a dermatitis similar to that seen in zinc or biotin deficiency.
  • EFAs are modified to make:
    • the classic eicosanoids (affecting inflammation and many other cellular functions)
    • the endocannabinoids (affecting mood, behavior and inflammation)
    • the lipoxins from ω-6 EFAs and resolvins from ω-3 (in the presence of aspirin, downregulating inflammation)
    • the isofurans, neurofurans, isoprostanes, hepoxilins, epoxyeicosatrienoic acids (EETs) and Neuroprotectin D
  • EFAs form lipid rafts (affecting cellular signaling)
  • EFAs act on DNA (activating or inhibiting transcription factors such as NF-κB, which is linked to pro-inflammatory cytokine production)
  • Fats play a vital role in maintaining healthy skin and hair, insulating body organs against shock, maintaining body temperature, and promoting healthy cell function.
  • Fats also serve as energy stores for the body, containing about 37.8 kilojoules (9 calories) per gram of fat. They are broken down in the body to release glycerol and free fatty acids. The glycerol can be converted to glucose by the liver and thus used as a source of energy.
  • Fat also serves as a useful buffer towards a host of diseases. When a particular substance, whether chemical or biotic—reaches unsafe levels in the bloodstream, the body can effectively dilute—or at least maintain equilibrium of—the offending substances by storing it in new fat tissue. This helps to protect vital organs, until such time as the offending substances can be metabolized and/or removed from the body by such means as excretion, urination, accidental or intentional bloodletting, sebum excretion, and hair growth.
  • 1
    But you can get the required amounts of essential fats from vegetables alone. Cooking oil causes heart disease, even olive oil will damage your arteries: youtube.com/watch?v=b_o4YBQPKtQ People who don't use oils do a lot better than people on the so-called "heart healthy Mediterranean diet: Commented May 24, 2016 at 18:20
  • nutritionfacts.org/2014/11/11/… "Out of 632 autopsies in Uganda, only one myocardial infarction. Out of 632 Missourians—with the same age and gender distribution—there were 136 myocardial infarctions. More than 100 times the rate of our number one killer. In fact, researchers were so blown away that they decided to do another 800 autopsies in Uganda. Still, just that one small healed infarct (meaning it wasn’t even the cause of death) out of 1,427 patients. Less than one in a thousand, whereas in the U.S., it’s an epidemic." Commented May 24, 2016 at 18:21
  • 1
    @Count Iblis The question was regarding veggies with no fat and low carb content. This would mean no fatty veggies (which are extremely healthy btw! Avocado is amazing!)
    – Othya
    Commented May 24, 2016 at 18:34
  • Hello. Although you showed the dangers of not including fat in the diet, you still did not say wheather protein(with fat removed) could be use as the sole main source of energy(required calories) for the body. Btw will the answerer/answerers see this update and reply? Thanks Commented May 25, 2016 at 19:29
  • 1
    You can't boil fat out! Boiled chicken breast is still about 22% fat by calories. Fat is also found intracellularly, as well as all cell membranes. Commented May 27, 2016 at 21:01

We have evolved to eat meat, vegetables, dairy etc. The closer these ingredients are to their original form, i.e. less processed and chemically amended purely for marketing purposes, the better. We also evolved to eat fermented foods, including (sourdough) bread and pickles of various kinds. We need protein, vitamins, minerals and various trace elements. Our bodies are pretty good at self-regulating and sometimes even filling in some deficiencies in diet, but the diet must not be synthetically limited or deficiencies can develop into problems. Our digestion and processes that feed all our cells are highly complex intertwined chains of processes. Just as you can't feed plants with large dose NPK fertilizers and expect healthy plants, you can't feed humans with a large dose of protein + one or two other thing and expect healthy humans. The often used analogy of an engine is much miss-aligned with biological processes.

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