If the women involved are talking about losing weight, they eventually will find that someone at some time somewhere will say something about their change in weight or eating habits which seems to indicate that they disapprove in some fashion. It can be a criticism of the fact that they are losing too much or that the methods they are using are unsustainable. It can be a comment about how they look worse in some fashion at a lower weight.
The response to this is usually that they make these comments because they are jealous. I think this is actually a type of projection. Projection is when you take your feelings and project them on to others rather than assess or evaluate the situation more objectively. The person saying, "my friend is jealous" is thinking that if she were in her friend's shoes, she'd be jealous if the friend was losing weight. Instead of considering her friend's true motivations, she simply assigns her own thoughts to the friend.
While it is certainly possible that jealously is a motivator, I think it is a narcissistic conclusion that is reached too early and often. People tend not to think about you as much as you think of yourself. They think of themselves. They are definitely uncomfortable with the changes you are making and the changes in you, but this does not mean that discomfort is driven by jealousy. More often than not, it is simply a change in the status quo that may trouble them.
People dislike having their worldview substantially altered or challenged in any way because it creates pressure in them to change, and change is hard and uncomfortable. Even if that change is no more than re-assessing your physicality, it creates discomfort. This is almost certainly part of our nature as humans. Seeing people change in appearance is alarming. To the parts of our brain that developed for survival, it may indicate illness, a change of tribes, or that you are even a doppelganger sent to fool someone and infiltrate their group for destructive purposes.
If part of their view is that you are fat, then having to accept you in a different body with different life choices means they relate to you differently. They'd rather you stayed the same so that they could continue as they always have in the way in which they handle you. It doesn't help, incidentally, that people who lose weight can be so obsessed with food and exercise that it often isn't only a bodily transformation, but also a personality one. Is it any wonder a friend might make negative comments about a person losing weight when they are mentally mired in little else? The person who once discussed music, movies, or books with you now can only think about their food limitations and exercise goals.
More often than not, thin people or people who are reducing their weight think heavier people are jealous of their success or figures. They think this because they are often jealous of "skinny girls", and they believe you must be as well. In essence, they believe everyone values what they value, even when they freely profess otherwise. If I think it's important to be thin (with the unspoken collocation "and attractive"), then you must, too.
If you don't say being thin ("and attractive") is best and what you desire deep down inside, you're simply hiding your true feelings. This thinking is not only part of the self-centered nature of all people which we must constantly battle in life, but also a way of validating the immense energy invested in the weight loss process. If you don't convince yourself that it is "worth it", then you may not continue.
This application of ones values and worldview to others doesn't apply just to weight, but to religion, politics, and every other aspect of our existence. The bottom line is that, by default, we all believe all people should mirror our values, and it's only some sort of distorted worldview based on your neuroses that cause you to be out of sync with "me". A person must try hard in most cases to step away from this tendency to impose their values on others. It's a very difficult thing to do, particularly at a deeper level as it means you have to give credibility to diametrically opposed views of your own. It's hard not to do that and feel insecure about what you value.
If those who are losing weight had true empathy for other people's feelings or perspectives, the first response would not be "you're jealous of me," because that is an indication that you are central to the thinking process. You're not. Others are doing what you are doing and that is thinking mainly of themselves. A more constructive first response would be, "my friend is uncomfortable with my life changes" and most productively a discussion of how what they said makes you feel and exploring their feelings would be best. Rather than jumping to the "jealousy" conclusion, seek the reality. It may be that they are jealous. It may very well not be so.
I didn't form the idea that dieting fatties are jealous of thin women based on my psychological insights into the psyche of fat people. Frankly, I think a lot of fat people, especially those over 35, are not envious of thin people. They simply want to escape the pain and difficulties associated with being in their bodies (both physically and from society's prejudice). I'm not jealous of people thinner than me at all. Their bodies have nothing to do with mine and indeed I do not want their bodies. I want my own body at a weight which is healthier and more conducive to fitness and mobility and that does not draw unwanted and cruel attention.
The basis for my idea that some fat women who are trying to lose weight are jealous of thin ones is because they say they feel so. They say it often. They say it with resentment and meanness sometimes. They talk about "butterfaces" and how they see skinny women with cute guys and that they believe they are more attractive than those women and could steal the men away if they were thinner. They're jealous of skinny girls because they have completely embraced the idea that their value lies in their bodies, and they want that thing of value that others have. The bottom line though is that they want power and they think skinny girls have more of it.
Of course, this is an illusion. I will grant that beauty (which is associated with thinness) brings power, but that power is of dubious value. It's the ability to buy something which you may not actually want to possess. Would you want a boyfriend or husband who valued you based on appearance? Would you want friendships because of perceived beauty? A lot of women who have said, "I'm fat and I'm happy with the way my life is" don't want what beauty and being thin buys them. They have internalized the idea that it's like buying a great looking sports car that will break down the moment something changes. Part of the bodily acceptance movement is rooted in knowing and embracing the idea that power should not be assigned based on body image. They refuse to be a part of it.
Because some women who are losing weight value thinness so much, they think that the aforementioned point is a load of hooey. They think it's just jealousy and bitterness on the part of fat acceptance (FA) advocates or that they feel threatened by their success. I have never thought that FA was driven by jealousy, but there may be something to the idea of feeling "threatened".
Part of the reason fat advocacy bloggers are so anti-diet and weight loss is that they have a worldview which is undermined by successful "dieters". Most fat acceptance bloggers are doing what they do because they feel they absolutely cannot change their lot in life in regards to weight (and maybe they can't) and do not want to be abused for a situation they are convinced is unalterable. If other fat people lose weight, it threatens that mindset, so they have to undermine the credibility of the process of weight loss. Fat acceptance bloggers aren't jealous of those who lose weight, but rather their mindset is threatened by your success. It's not about you. It's about them.
What's the point of this post? My point is not to jump on the "jealousy" label so quickly when people deal poorly with your weight changes. It is an attempt to diminish them and it reveals your self-involvement and sense of superiority over nothing more than how much you weigh and what you eat. And, ironically, that really is the sort of thinking from others that we're all trying to escape by losing weight.