I have realized in the past couple of days, people who were vegan but chose to go back to eating meat due to feeling tired/lethargic when they do heavy physical activity(such Anne Hathaway), many of them were probably suffering from iodine deficiency.
Iodine deficiency leads to a lower thyroid function, which leads to a low metabolic rate that can cause weight gain and fatigue. This could be why many people find it hard to lose weight even on a vegan diet.
When Anne Hathaway went back to eating fish from her vegan diet, she said she immediately felt more energy. Fish contains lots of iodine that could have resolved her supposed iodine deficiency. Even though fish contains creatine that could also contribute to higher energy levels, the iodine would have a greater impact in increasing energy levels especially if the person is suffering from iodine deficiency.
I have heard of many people who started on the vegan diet and then complained of feeling tired, especially for vegans who do lots of fitness. Many of them probably suffered from iodine deficiency and needed to take iodine. Vegan sources of iodine include iodized salt, seaweed, kelp and bottled supplements.
The next time you hear of someone complaining they feel tired after starting a vegan diet, do them a favour and suggest that they take iodine supplements quickly.
(Fat is also important to maintain hormonal balance to feel energetic. I heard from a vegan on the 80/10/10 diet who started taking fat said that she felt much more healthier. Sodium functions as an electrolyte and is also important to maintain energy levels. Taking creatine supplements can also increase the energy transport within the body.)
Iodine – The mineral that charges your energy battery