&gt; <i>But what if the car adjusts its fuel efficiency dynamically?</i><p>And your body does just that. That&#x27;s why you continually re-evaluate what your calorie needs are and adjust your intake accordingly. Weight Watchers does this every single week. See how much you weigh, figure out what your &quot;maintenance&quot; calories are, and make sure you eat 200-300 less than that.<p>Then, yes, your body changes, adapts and becomes more efficient, because you&#x27;re changing things, and it&#x27;s getting lighter so be definition it needs less calories. So then check-in again a week later repeat. And repeat. And repeat.<p>&gt; <i>If certain levels of caloric deficit can cause physiological changes that affect rate of weight loss</i><p>I wouldn&#x27;t go there. I mean, if you want to change the rate of weight loss, just eat absolutely zero calories for 6 months. I grantee you&#x27;ll lose a massive amount of weight. Is that a good idea? absolutely not. There is an amount that&#x27;s sensible and works well. It&#x27;s something like 200-300 less calories than your maintenance requires.<p>&gt; * Why not maximize efficiency of weight loss*<p>It&#x27;s interesting to me you&#x27;re still viewing this as &quot;weight loss&quot;, and something to be maximized and made more efficient, and something with an end date. What hasn&#x27;t dawned on you yet (and usually takes most weight watchers people a very long time to get) is that, at some point in the future, you will weigh your goal weight. When you get there, your calorie requirements to maintain that are going to be massively lower than they are now. Actually, they&#x27;re going to be right around what you were eating the week before you got to your goal weight. Guess what? That&#x27;s now what you&#x27;re going to eat for <i>the rest of your life.</i><p>You can&#x27;t really maximize the efficiency of <i>the rest of your life</i>. So just start working towards it, <i>today</i>.