Which is the specific heat of human body?
A specific heat for humans typically quoted in the literature is 3.5 kJ/(kg K) (for example, pg 16 of Herman's "Physics of the human body", 2nd ed).   This is below the value of water (4.2 kJ/(kg K)) primarily due to body fat, which has a lower specific heat than water.

Despite its title, the article:

Faber and Garby, "Fat content affects heat capacity: a study in mice", Acta. Physiol. Scand., 1995, 153, 185-187, https://doi.org/10.1111/j.1748-1716.1995.tb09850.x

contains a brief summary of the literature concerning the average specific heat of humans.  The authors find that the specific heats of lean and fat mice agree reasonably well with a relationship originally proposed for humans:

$$ c_P = (3.72 - 1.84 \: m_f ) \text{ kJ/(kg K)}$$

where $m_f$ is the fraction of body fat by weight.  Wikipedia  ( https://en.wikipedia.org/wiki/Body_fat_percentage ) indicates that body fat percentage (by mass) is 17-21% and 25-30% for "average" men and women respectively (both neither "fit" or "overweight").  Substituting $m_f = 0.22 $ into the formula above gives 3.3 kJ/(kg K), in rough agreement with typical value of 3.5 kJ/(kg K) quoted in the literature (the literature value corresponding to $m_f = 0.1$, a value typical for a male athlete).

There is some uncertainty in my mind about the accuracy of the formula above, as it is based on a heat capacity of fat significantly smaller than recently reported (see database reference below).  However, I have trouble imagining a situation where the average specific heat capacity of a human would need to be known to great accuracy (it is needed for the artificial, but instructive Problem 1.54 in Schroeder's Introduction to Thermal Physics).  On the other hand, the heat capacity of various components of the human body could be of significant utility (the influence of localized heating etc...).  These specific heats (blood, bone, etc...) are tabulated (with citations) in the "Tissue Properties Database"  http://dx.doi.org/10.13099/VIP21000-03-0 (V3.0).