Some popular beliefs attached to weight loss have been shown to either have less effect on weight loss than commonly believed or are actively unhealthy. According to Harvard Health, the idea of metabolism being the "key to weight" is "part truth and part myth" as while metabolism does affect weight loss, external forces such as diet and exercise have an equal effect.[43] They also commented that the idea of changing one's rate of metabolism is under debate.[43] Diet plans in fitness magazines are also often believed to be effective, but may actually be harmful by limiting the daily intake of important calories and nutrients which can be detrimental depending on the person and are even capable of driving individuals away from weight loss.[44]
Unintentional weight loss may result from loss of body fats, loss of body fluids, muscle atrophy, or even a combination of these.[25][26] It is generally regarded as a medical problem when at least 10% of a person's body weight has been lost in six months[25][27] or 5% in the last month.[28] Another criterion used for assessing weight that is too low is the body mass index (BMI).[29] However, even lesser amounts of weight loss can be a cause for serious concern in a frail elderly person.[30]
Onesicritus also mentions his colleague Calanus trying to meet them, who is initially denied audience, but later invited because he was sent by a "king curious of wisdom and philosophy".[108] Onesicritus and Calanus learn that the yogins consider the best doctrine of life as "rid the spirit of not only pain, but also pleasure", that "man trains the body for toil in order that his opinions may be strengthened", that "there is no shame in life on frugal fare", and that "the best place to inhabit is one with scantiest equipment or outfit".[107][108] These principles are significant to the history of spiritual side of yoga.[107] These may reflect the ancient roots of "undisturbed calmness" and "mindfulness through balance" in later works of Hindu Patanjali and Buddhist Buddhaghosa respectively, states Charles Rockwell Lanman;[107] as well as the principle of Aparigraha (non-possessiveness, non-craving, simple living) and asceticism discussed in later Hinduism and Jainism.[citation needed]
The spiritual sense of the word yoga first arises in Epic Sanskrit, in the second half of the 1st millennium BCE, and is associated with the philosophical system presented in the Yoga Sutras of Patanjali, with the chief aim of "uniting" the human spirit with the Divine.[24] The term kriyāyoga has a technical meaning in the Yoga Sutras (2.1), designating the "practical" aspects of the philosophy, i.e. the "union with the supreme" due to performance of duties in everyday life.[25]