The prophet is commanded to perform a symbolic, tangible action that illustrates the harsh reality destined for Jerusalem during its siege. The focus shifts from his physical posture to a daily survival menu, designed to mirror the severe famine that the city's residents will soon experience. The required ingredients include wheat, barley, beans, lentils, millet, and spelt, making up a mixture of various grains and legumes [מצודת ציון]. Under normal circumstances, each of these crops is prepared and eaten separately [ביאור שטיינזלץ]. Beans and lentils, in particular, are not typically used for baking bread at all, except in times of extreme starvation [רד״ק, אברבנאל]. The prophet is instructed to grind this entire mixture into flour and knead it together in a single bowl to make his bread [אברבנאל, ביאור שטיינזלץ].
This preparation serves as a grim sign for the Israelites. It indicates that during the siege, a severe lack of clean food will prevent them from separating high-quality wheat for their meals. Instead, they will be forced to mix it with inferior crops, resulting in a low-quality bread that will be eaten with disgust and a complete lack of taste [רש״י, רד״ק, מצודת דוד, מלבי״ם].
The duration of this diet is set for three hundred and ninety days, corresponding to the time the prophet lies on his side. The primary approach among commentators is that while this number specifically reflects the days spent on his left side, it implicitly includes the additional forty days he spent on his right side, as the siege and starvation persisted throughout the entire period [רד״ק, מצודת דוד].
However, other scholars maintain that the timeframe is exactly three hundred and ninety days. According to one perspective, unlike previous prophecies where days represented years, this number reflects a literal period of about a year and a month during the siege when the famine was truly unbearable, which is why the additional forty days are omitted [אברבנאל]. A complementary historical view explains that the Babylonian army had temporarily retreated from Jerusalem to face Pharaoh's forces. From the moment the Babylonians returned to resume the siege until the city's eventual destruction, exactly three hundred and ninety days passed. The inhabitants survived on this poor, mixed bread only during this specific window because afterward, the food supply was entirely exhausted. In the final forty days before the city walls were breached, the people suffered from total starvation and death, meaning there was simply nothing left to eat [מלבי״ם].